Curses do not stack with those cast by another warlock.
All Warlock curses are instant cast, have a 40 yd range and no cooldown.
There are only 2 improvements that specifically affect curses:
- (Affliction talent, Tier 2): Your also effects up to 15 nearby enemy targets within 20/40 yards of the cursed target. Also, your reduces the target's energy, rage, focus or runic power generation by 5/10% while active.
- (Minor glyph): Increases the range of your Curse of Exhaustion spell by 5 yards.