Now that I've finished my first draft of all the monsters I intend to put into my "Monster Conversion Document" I need to go back and see if I can't find some more interesting ways to vary them. Dex drain might become slowed for instance, while diseases might inflict some more unusual effects like blind or possibly confused (to represent delirium).
This, presumably, is one reason the monsters in 4E all have seemingly-random tactical effects like "shifts five feet when attacked" or "teleports six squares when rolls a 20" or whatever, to give them some kind of interesting wrinkle without adding math to the fight (which is what all those poisons, diseases, miss chances, stat drains, and so on used to do). While I applaud the sentiment, I can't help but feel that too much of this takes you solidly into the realm of lasersharking, a term which I just recently encountered but which describes 4E precisely.
The key is to find balance. There's no reason to give Joe Goblin a funky power; he's a just a goblin fer cryin' out loud. But those creatures that do have an unusual ability, need to do something besides just "moves you down the condition track" over and over. Besides the fact that it can end a fight much more quickly than desired (by sending the PCs into a death spiral), it's just dull.