warlock:
+not many of them are around (especially at roc of what ive seen)
+fast grinding
+good PT help
+Stunbuff for 2friends
+Shield
+very good at taxi (if spots are free, dont know current situation, just know that Warlocks are the best taxi drivers from Csro

)
-PvP against HW/HS is hard...
-boring skill animation
cant think of more negatives....
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i have to agree Jadekiss, if you want a Wizard/Cleric, then just farm a new char up, that will be faster and you wont wish you warlock back after changing to wizard...
i also think that warlocks are very much more needed at high Uniques than Wizards, (warlock -> more dmg of wizards+ Unique becomes stunned even more often stunned (imagine 6 warlocks at roc (wouldnt be many...) so 12 guys got stun buff-> 12* 35% per hit of roc for being stunned at his big shout)
Keep the Warlock!