After leaving the game right after Cataclysm started I recently returned and have been playing my Warlock and my Mage. Both play really well in PvP and seem to fill different roles really well. Warlock basically needs a portal and health stone as well as peeling and healing in group settings.
Affliction can't seem to kill any one on its own in group settings but is tough to nail down with support.
Frost is a solid spec, great control and very hard to nail down even with help, easy to keep up by healers but Spell Steal costs a ton of mana. Setting up the burst rotation is super easy and hits like a 10 ton truck, invisibility pretty much guarantees an opener which is a huge advantage. Fire is a monster, puts out great damage and loves to play in melee range -much like Frost just hotter, pun intended.
Warlock feels like a support one-trick pony, Unstable Affliction to cover your DoT and fear spam, seriously? When I played Affliction it hit hard as hell, if I got a full DPS rotation on some one it was pretty much over for him if they didn't heal! At 80 Unstable Affliction crit for massive amounts! Affliction had burst and crit meant something!
I tried Destruction, Immolate dispel is annoying as hell, and as soon as the other team realizes I'm destro I become public enemy number 1 lol I tried Demo and its fun for laughs against PuG BG melee and hunters or send it after a Mage and pop CC immunity and watch the mage get shredded but does little in group team play.
Mage both Fire and Frost seem to have really cool things, seems to bring so much to the table. Control, mitigation, burst and utility.
I guess the Warlock I knew and loved is no more!