Locks are very, very useful from a utility standpoint. They're also very nice for being able to run away from someone while dotting them up. 4x pet tanks are hugely useful in PVP and felguards are lethal to rogues who pop Cloak of Skill thinking it'll work on you like it does on solo squishies. Seed of Corruption is also a very nifty ability. Downside to them is the lack of burst damage when things get hairy, IMO. I'm rolling up a 4x mage team to see how they compare in PVP.