I have 4 locks and a priest and love them. I went in demo to get felguard and working my way down affliction to get more DOT dps. I use (for super easy and lower), 2 succ, 2 imp, (for slightly later and medium hard), 1 void, 1 felhunter, 1 imp and 1 succ all with improved talents, (for really hard) I use 2 voids (those chars have more stam), 1 felhunter and 1 imp until level 50 or so. Then I use 3 felguards and 1 felhunter. After I got felguards, I have only use voids once (I was lvl 61 or so and the outside elite in Hellfire Penn. scared me. I might have made it with just felguards, but I wasn't sure and didn't want to wipe and try it again.

2 of my chars are heavy stam (eagle, whale, whatever I could get that had good stam and something else), and the rest have mostly owl gear. Later (Outland and above), I moved the felguard locks into stam type of gear and the priest and felhunter chars into mostly spirit. I haven't had any problems with almost anything. Yeah, I have to lifetap with mana feed talent once a fight, but have no downtime because of it (felguards holy hell drink mana). I wish the pets were as strong as hunter pets, but I can heal them like super crazy (healing talent also gives 30% protection to pet). I don't PVP with them, cause the pets would never get the people's enough aggro to keep melee off me. Also the felhunter no longer helps with stealthers. All wearing cloth and I would be taken out by one whirlwind bezerker (non-fearable) warrior.

Hope that helps and good luck.