Keep in mind divine hymn tooltip has been around since Ulduar; before haste increase tick counts. In my opinion the tooltip only mentioned a maximum of 12 ticks to reinforce 3 x 4 = 12.

Sorry for noob question, but I do recall reading somewhere, that PI doesn't stack with BL?

It doesn't. Haste modifiers by % do not stack (Icy veins, PI, Heroism, etc.).

Just checked - they don't. Got hero from a shaman, popped PI, no change in spell casting times.

There is some talk about "shield spec" over at Disc discussion, so i was wondering which fights favour extensive shield use and how does the shield spec actually play?

Also another question. My disc priest has found himself in a tank healer position for an 8/12 normal 10-man raid, and he is only wearing 5-man heroic and rep gear. At the moment, his gear is heavily mastery-oriented, so i am considering a different secondary stat combo. Which combo do you feel works best for a tankhealing Disc priest in blues?

Does anyone have a good idea how to analyse the amount of targets I hit with PoH on average? I'm not sure about the WoL files since they list and overhealing but I'm not quite sure if a target is considered to be overhealed, if it's out of PoH range. And I can't find a raw number of casts to compare with the hits...

Infight: Get MikScrollingBattleText or a similar addon and set up a display for your healing done with a spam filter that consolidates many hits of the same spell.
The result is something like this: "54823 (5 hits, 1 crit)"
Some pitfalls: Pets count as well and if you've set the incoming heals on you on another display you won't see yourself in the "n hits" number.

Combatlog (World of Logs): Select the fight, open the expression editor and enter:
You'll get a list of all the Prayer of Healing spells you started casting. Then just copy&paste the list (don't forget the next pages) into an editor with line count and check how many lines you pasted.
Pitfall: For some reason SPELL_CAST_SUCCESS (fulltype 601) doesn't work for casted heals, so we're reduced to SPELL_CAST_START (fulltype 601). That means that casts that we interupt or that get interupted end up counted as well.
A better method would be to parse the log for Prayer of Healing heals that happen within a short timespan. That would require some scripting though.
If you don't have to do it for many logs you can just set fulltype to 301 (SPELL_HEAL) and count them yourself, but that will take time.

Oh and no, WoL overhealing is overhealing that happened because the heal healed more than the target was missing. If someone is not in PoH range you won't get overhealing or anything else that the standard WoL tracks.

The value of hit is roughly linear until cap. There is no soft plateau where the next point of hit is worth relatively less than the last.

Most priests here will recommend capping hit asap. It may not be the best secondary stat according to spreadsheets and simulators, but it's very close, and capping it removes a source of player error. More than likely, in real situations, your DPS will increase with capped hit.

Halfus is a fight that favors disc due to the MS component. Shields aren't affected by it and Grace allows you to effectively reduce the debuff level for your heals. Also, the +dmg modifier in the fight makes your Smite spam more effective (in terms of DPS and healing). Magmaw is a good fight as Disc for the same reasons.

Nefarian favors disc over holy due to barrier alone. Smite spam is very effective during the platform phase as a steady heal to your team. Chimaeron is nice as disc due to A/A burst on the feud phase paired with barrier as well.

I like the idea of Disc during the twin dragons for the burst healing via archangel and to barrier a blackout or two but find that in practice that holy makes a very strong showing when theralion is down due to the high raid damage.

As for actual play style - you are going to Smite the tank's target. This will spit heals out into the players clustered around the mob. If the tank is taking more damage than that passive healing returns, you PW:S the tank, Penance, Gheal (I drop a Renew, too usually) and go back to smiting. If the tank requires sustained healing, pop IF, cast Gheal and start the rotation of shield, penance, gheal again.

If you've got A/A stacks, you can use that to burst your healing for 30 seconds.

Group healing is very similar. Smite your way into 5 stacks of Archangel if possible, pop A/A, Inner Focus, bubble someone - PoH, Penance someone, PoH. You can use barrier if your group is stacked up.

The key to disc is Penance for Grace on your healing target and then PW:S for Borrowed Time to get a bit heal off quickly. That is more or less how it works, but you'll vary it according to your raid role.

Given now that the Chaotic metas have been fixed, is this now the preferred meta for Shadow, or are we to stick with the Ember? I'm, unfortunately, not terribly good at running SimC just yet, so I'd appreciate if someone with more knowledge could run the numbers.

Worth noting that atonement double dips when you have engulfing magic - you get a 100% buff on the damage portion, then a further 100% buff on the healing portion, giving 400% atonement heals. It's incredibly powerful for healing up the tank and any melee.

Here's a excerpt of my log from last fight (10N):

Notice how the atonement heals ramp up hugely during engulfing magic, and also how it bypasses the atonement cap.