My cliff notes on the role Mages will play in raiding in Cataclysm. I know Fire/Arcane the best, so I may have it all wrong for frost.
General Buffs
Time Warp at Level 85, a 30% haste buff for 40 seconds. Arcane Brilliance, mana and spellpower boost.
The Good: Arcane mages bring steady single target DPS and a phenomenal burst DPS that can be deployed in a bosses moment of weakness to make them QQ warlock tears. They bring a single target +3% crit bonus, and a raid-wide +3% to damage done.
The Bad: If they screw up their evocation, they lose a major component of their burst DPS.
How to spot a good Arcane mage: they have Mage armour equipped and glyphed and keep their mana at 85-100% until evocation/mana gem come off cooldown, then they pop the gem and go nuts on DPS for 10-20 seconds, then back to maintaining 85-100% mana.
Fire
The Good: a fun spec with good single target DPS and the potential for amazing AoE damage. Even stronger when the boss is below 35% health, just in case you were wondering who deserved the battle rez. Provides +5% spell crit chance for the raid. Cauterise gives amazing survivability, and improved mobility will increase contact time. Better yet, you can go OOM and still do damage with a combination of mana free Scorch and mana free Pyroblast.
The Bad: Ignite is still buggy, and the spec is very dependent on crit (and luck) for damage. Living bomb only hits up to 3 targets, can be accidentally overwritten for major DPS loss and interacts with Impact procs in counterintuitive ways (impact spreads damage to adjacent mobs, see the 3 target limit for why this is a problem).
How to spot a good Fire mage: it’s all in the use of the Combustion cooldown, which combines all existing DOTs into one mega-dot, so a good fire mage will wait for all three of their DOTs to be rolling on a target before pushing this cooldown.
Frost
The Good: a permanent pet! Mana replenishment for the raid. Competitive PvE dps for the first time since A’lar in Tempest Keep.
The Bad: Frostburn can be too bursty, so some threat generation issues on pulls (yes, thats right, frost mages can now do too much damage, inconceivable!). Almost no useful off-spec talents to spend points on. Pet is so awesome it may have mana issues from doing too much damage…
How to spot a good Frost mage – they cast in the following priority list:
1.Frostfire Orb, if cooldown is up.
2.Deep Freeze, if cooldown is up and Fingers of Frost is active.
3.Frostfire Bolt, if Brain Freeze is active and Fingers of Frost is active.
4.Ice Lance if Finger of Frost is active.
5.Freeze, if cooldown is up, Deep Freeze cooldown is up, and Finger of Frost is not active.
6.Frostbolt.
Mechanics Are Easy 