To add to the Nibelung argument i've tested and noticed that the damage they do doesn't scale up with various buff.

In my guild i'm one of the first target to be bitten by BQL and the Valkyrs still have their static damage, while having an additional haste/crit would benefit more of the debuff. On LK on our try before the first kill they ended up shotting the low life Drudge Ghouls and wasting the plague on them.

End of the story, on fights like Festergut it may be usefull to use it if you have no better combo (another staff or mh/oh).
On fights where you get a damage "buff" of any sort or when you have to do focused burst on targets (Twin Valkyrs, BQL, Lich King, Putricide, Sindragosa) you'll end better using other weapons.

Val'kyrs scale with debuffs -- same as mirror images -- and cannot be affected by buffs (such as bloodlust). Thus, they benefit from Curse of Elements (or other equivalent 13% magic damage debuffs) and possibly Totem of Wrath's 3% crit (since that is a debuff). But yes, that is an excellent point duloth. Not only do Val'kyrs die prematurely on Blood-Queen, but they will hold you back on the 100% damage boost.

I think Rawr actually has them doing less damage than they really do. It's listed as 27,008 unbuffed damage. In spell damage breakdown, it's listed as 94,421.54 with 3.13 hits (on a 5 minute fight, using Fire). This works out to 30,166.62 damage per hit. However, 27,008*31.13 = 30,519, which means total damage for 3.13 hits should be 95,524.59.

I'm not entirely sure if there are any other debuffs I'm missing either. Most magic damage increases are buffs, not debuffs. Regardless, [Nibelung] shows to be slightly ahead of [Illumination] (22.11 DPS difference) in my 10-man raid setup, but in my 25-man raid setup, Nibelung is 31.9 DPS behind Illumination, and this is likely because of the scaling issue that Duloth mentioned. I have vastly more raid buffs in 25-man (Arcane Empowerment, Swift Retribution, Elemental Oath, Focus Magic, Totem of Wrath, and Misery. All of these make the passive crit/haste ever more lucrative. So that's definitely something to think about -- Nibelung gets 'better' the less buffs a group has.

I haven't seen anything here lately about patch 3.3.3. I am liking the change to Brain Freeze. Glyphed for the 5% bonus damage to Frostbolt now means that you can still slow mobs sometimes, with instant cast Frostfire bolts. I am thinking about the Saurfang where I am always a kiter, being a frost mage. It's probably best to always slow the beasts rather than hope for a Brain Freeze slow or Deep Freeze stun.

Speaking of that fight, I run it on 10s a lot. I park my Water Elemental somewhere out of the way as I am worried about it being too close to me or someone else. I can't do that on 25s. Is Blood Nova a concern for my Elemental, or can I stack it on myself in 25s without worrying about Blood Nova AoE damage?

The exact weighing of your stats can change very quickly depending on your current gear. From what I've seen so far personally, crit has always been more valuable for me then haste, but 23 Spellpower in a red socket still wins out slightly. That is under a situation in pretty much fully arcane-balanced gear, so I have a somewhat big deficit on crit. If I would be able to get a big crit-boost, like Muradins Spyglass, this might actually change quite quickly, since the numbers are really not far off.
In the end, as always, this is the exact question that Rawr is made for. There is no overall, 100% viable rule for the balancing of stats, but Rawr can give you pretty precise data based on your gear and usual raidsetup. Use it.

On a more practical note, I personally simply keep my SP/haste gems in use. If you are raiding in PvE, and want to be able to provide the benefits of an arcane specc ocassionaly, its a good idea to keep your gear versatile. SP/haste might be a tad bid worse for fire then SP/crit, but the difference is slim. SP/crit for arcane on the other hand is a pretty terrible choice, so by socketing it, you'd be spoiling your arcane-gear.

Another effect of crit gem (and the stat as a whole for trinkets ect) is the reduced rng. It was so long since I played fire that I totally forgot how rng can affect your dps, the variance on short fights, depending how often you crit and the amount of 2 crit streak is quit painful (It's a matter of choice here but I hate rng).

At 50% crit the variance is maximum, then every crit % you gain reduce the variance. Closer you are from 100% smoother is your dps.

Alright, I did a little clean-up of the original post since the Cataclysm class changes will come up tomorrow. One of final changes that had been missing was adding that (Enhancement) Shaman trigger Torment the Weak in raids with Earth Shock.
When updating the post however, all the item links went kaputt, not sure how valid item links are made now.

When someone with beta acces opens a new thread for Cataclysm mechanics, feel free to copy information from this post and thread for an easier start with a short mention or reference. I feel a bad already that it took me until now to add a little acknowledgement to this post for the countless contributions of named and nameless authors.