As far as I know all health healed by VE is turned into threat to the spriest. All mana returned by VT however, is counted as threat to the receiver of it.

VE is the thing I drop first, when threat is capping my dps. In Karahazan this usually is not a problem at all, so I keep VE up, just to be nice to the healers who get nervous because of my SWD crits.

Shackling is of almost no concern to dps (use a focus macro!), but especially on trash I need to go full out on the SWD/MB cooldowns to keep up with the other dps classes like BM-hunters, locks and mages.

And yes, keeping up your DoT's is the most important thing to do on bosses. That's where I tend to slow down on the SWD's, because I was a healer before I got lured onto the dark side.

When I'm lazy, at the Prince, I keep just at 40y alongside the mages, and keep SWP an VT up on the boss and blast a MB every cooldown. This still nets me almost 600dps which is enough in a good group. On easy bosses like Attumen, I get almost to 1000dps by using VT, SWP and MB. Think I could easily get higher if I start SWD'ing as well.../flex

If you do 1000 DPS your regen 50 mana per caster per second resulting in 125 tps. Not negligible but considering 1000 dps is several hundreds tps already it's not that big. On AOE fights where everyone take damage VE generates 5 times as much threat as VT which is where it gets significant. While shadow priests get extra threat from VE/VT you have 25% threat reduction from talents while mages/warlocks get 10% and do less DPS overall. So unless you're VE healing you should generate threat aggro slower than mages/warlocks in general with equal buffs. Of course mages/warlocks can also clear their aggro making things much easier for them in the long run when aggro is a problem. Anyway not using VT is out of the question anyway. VE should be manageable as well especially if your healers are actually doing their job and VE is just topping people off (shouldn't ever let VE heal big damage anyway as you risk the player getting hit again and dying). If your tank is doing under 800 tps tell him to step it up, if he's doing under 600 get a new tank.

First, to truly maximize one's dps on trash pulls, avoiding the use of VE on some trash pulls is acceptable. However, on pulls which you know the group will be taking damage (ie the ghost pulls after the Shade of Aran) it is invaluable.

Assuming the priest in your group is properly spec'd and has 3/3 Shadow Affinity he should be generating 25% less threat, and thus the slow healing he will be doing to the group should be neglegable toward his threat generation (assuming he is not having problems with that)

On the vast Majority of boss fights however, VE should almost always be used as the heals done by VE serve as a constant, weak HoT on the group. On the level that VE functions as a HoT for the group and it's overhealing doesn't generate threat it should be up at all times. The GCD associated with it every one minute is not going to be detrimental to your dps. Personally, to get a good dps lead in the fight, i save my GCD's as much as possible and skip VE for the first part of some boss fights (also note that the loss of VE to start the fights also reduces your threat generation significantly for the start of the boss fight. Typically being in a warlock group or even healing yourself from SWord Death is still invaluable threat reduction.)

Second, from what I have learned and observed, there is little to no threat associated with mana returns. A lot of people associating their threat generation may be attributing the threat with the shadowmend from the 3/3 FSW set bonus (though I am not certain that generates threat, it is just a theory).

Third, using VE should be done without hesitation. Though you may have the healing to keep up the group and tanks, check how much healing the priest will do spread out over his/her entire group. It is invaluable to have up, and also can generate mana as well as to paladins who have been hit by some sort of group damaging gimmick. On trash pulls it may not always seem to be worth the global cooldown, if you can spare it, its certainly worth throwing up. At the very most you lose a mindflay or mindblast/death cast time.

Fourth, as for damage, it really depends on not only the priest, but also the group. In endgame gear from what I have observed not only from the guild(s) I've been in, shadow priests toward the endgame content don't have quite the dps of good rogues/mages. However, with a warlock in the group, I again can only assume that shadow vulnerability is up on bosses or trash at some point, should give his dps a huge boost. Though shadow priests boost the entire group's dps with Misery, his own should be substantial as well. From personal experience, a shadow priest with almost 900 spell damage should be able to sustain at least 700-800 dps, and if he is coasting anywhere less than that, he/she is probably being sloppy. And, not to be harsh, but if keeping his eye on a shackled mob is really that detrimental to his dps he/she might want to consider beating a spell priority list into his/her mind so he can walk and chew gum, and do the group much more good.

He/she shouldn't be on the bottom of the damage meters, nor anywhere near it. Though, I would take into consideration the posts earlier, they were correct in stating that many pulls in karazhan are aoe based, and skew the meters. I also recommend watching boss meters, but keep an eye out on trash meters to make sure everyone is paying attention.

The most constructive advice anyone here could possibly give is to keep dots refreshed. I've seen talented players drop from top 5 to 12th on gruul meters simply because their DoTimer stopped working. It is imperative that you keep dots refreshed not only for your dps, but for the sake of the groups health and mana regeneration.

Personally, once you get the gear to pull it off, I would recommend spec'ing into the improved mb talent, and making sure you have 5/5 shadow power. Also, make sure you are hit capped (5/5 shadow focus probably with his gear - again, another assumption/educated guess), it is more important for you to be hit capped than to have more +dmg or +crit. Each time you get resisted your dps is ruined, or any rhythm you have may be thrown off (side note: each resisted shadow word pain is about a wasted 600 mana, the equivelant of three mind flays). I would recommend putting MB and Death as a priority, and keep them on CD as they are your highest dps spells, but the least mana efficient. Make sure you refresh a DoT before casting either one, as they are a huge bulk of your dps, and are worth prioritizing. Finally, mindflay is only a filler spell in between dots and blast/death. It is the most mana efficient spell in the game, as once you hit a certain gear curve your mindflay time is actually gaining you mana back. However, as mana efficient as it is, it is also your lowest dps spell. Use it only if you have nothing to refresh/put back on cooldown.

Edit: It would help us greatly if you could post his/her spec and gear so we could help associate a higher dps spec, or even a more effective one. Also, most shadow priests at endgame raid gear (or full tailors) can sustain over 1000 dps, 500-700 is not acceptable, even in karazhan. The reason that rotation suggested earlier lends itself to little use of consumables is simply due to the fact it is the most mana efficient possible, but also the lowest constant dps. You want to hit this high dps cap not just for the sake of high dps, but because you are returning the most mana to the group. You may need to chain chug mana pots on a boss fight with mashing MB and Death, but it will do the most overall good for the group/raid. Also, the TPS of mana returning (should it exist) is so minute is almost pointless to consider, the vast majority of your threat comes from doing damage and the healing done to the group.

Edit #2: Two days later - capitalized two I's (I hate you Kalk).

Something you might also wish to check on, is his spell hit rating. Ideally, he should have 76 to spellhit to minimize resists.

That's a very strange spec. I don't understand 8 in Disc, particularly if you're not getting Imp Fort. I also don't understand Imp Psychic Scream but not Silence which would still be somewhat useful at Karazhan level. Further, I sincerely doubt he has the mana to use MB on every cooldown before talents so putting points in Imp MB confuses me more.

MB and SWD are our critting spells. Crit rating is worthwhile, yes but it's hard to quantify how much crit is worth vs spell damage - with only 861 +damage it would be a very low priority for me.

Frankly, from what you're telling us the best thing you can do is point him to this and other forums that discuss how to play a shadow priest well. That spec and the gems you state he is using make it pretty clear that he doesn't understand a lot of basics.

Ironically I was just crunching numbers on this last night. With around 1300 spell damage buffed, the tradeoff seems to be roughly 8 crit rating = 1 spell damage, assuming you are using Death and Blast every cooldown. That's really bad but it's not technically worthless. Since it's so easy to hit the hit cap, it might be worth rating crit as a more valuable stat than hit.

I get a similar value, about 6+ CR to 1 SpellDamge.

Raid environment scaling.....

SimulationCraft/Scaling/Priest - Shadowpriest.com Wiki

Would this be a better build?

Talent Calculator - World of Warcraft

This forum community generally tries to dissuade "rate my build" threads, so I'm not going to comment further. I will suggest that you have your struggling priest friend review Armory profiles for any of the Shadow Priests commenting here if he's looking for opinions.

Helping you understand a good Shadow Priest build really won't help him perform better - he needs to do the learning himself.

Few observations about low +dmg shadowpriests:

Less damage amounts to less mana for more damage. As a result, MB and SW: D become less established in rotations (as they are low HPM -- high DPS, if sustained).

With the idea that MB and SW; D are less frequent in low +dmg rotations, the benefit of +crit is diminished. +crit is already "useless" to a shadowpriest, with respect to equal itemization points spent in +dmg. I've never seen a case where I would socket / purchase (on item) +crit over raw +dmg.

Furthermore, talents such as Imp. MB and Shadow Power become less valuable as stability of MB and SW: D casts decreases. Depending on latency and use of UI / stopcasting, I'd only recommend 1/5 Imp. MB to a low +dmg shadowpriest. I can't see a 4/5 rotation being sustained, even grouped with a resto shaman.

Correction; the data actually says 11 crit = 1 DPS and 2.2 spell damage = 1 DPS, so 5 crit = 1 spell damage seems reasonable.