I have played 3 locks through BC and WOTLK, and 5 locks through CATA. I must say the damage is not there to kill someone in reliable time, ie. before they get healed/heals themselfs. Sure it was fun to stack 5x dots and what not, but single pala or DK pretty much wipped most of the team anyway. Coupled with healer and I was toast.

I have played aff, destro, demo and have found demo to be the best for me, because I love the demons and the simplicity of spell casting. With demon form it was possible to burst something down, but without it I was pretty much walking dead. I switched to 5x Dks (I have played 3 DKs since wotlk) and never looked back. It was night and day.

I played locks in beta and it was not that fun as it was during previous expansions. I decided not to buy MoP, because I dont like where it went. I may buy it in the future, but right now all 5 accounts are frozen.

just my 2 cents.