Since blizzard has adopted the "bring the player, not the class philosophy", curse of weakness has lost its usefulness in PvE (and lets face it, next to no one specced into improved curse of weakness). So, here's an opportunity to give something to locks that may actually help PvP and can still have some use in PvE.
Here's my idea for the new curse of weakness:
Curse of weakness: w sec cool down, x% of base mana
Weakens the target reducing all damage done by y% for z seconds.
Simple. Locks get a useful PvP curse that may save them, it can't be spammed (thus affecting only one target). This spell would save a lot of locks from melee or even save a fellow healer. A curse with a cool down is nothing new, look at curse of doom.