I think it depends on what type of game you're playing. In my NL house game 3-5 X's the big blind seems to work in scaring people off but at the same time keeping one or two around. Sometimes I'll make it ridiculous, like 7-8 X's the big blind to make it look like I'm trying to steal, and I'll get called by a person or two. This works because the guys I play with make it a habit to raise huge when they don't want a call, they make it too obvious that "hey, I don't have crap, I'm just trying to buy this pot."

But online its a different story. In MTT's I'd say to raise it 3-5 X's the big blind, just like a house game. In ring-games, though, I guess it depends on what blinds you're using. In .01/.02 games you sometimes find tables where a .10 or .20 bet will get called by six or seven people, and you can be screwed. In this case you've just gotta bet huge on the flop to scare everyone away, if somebody calls or raises you're eff'ed.

I've also seen it the other way, where I've raised to .10 and everyone folds, and I pick up a weak .03. Just depends on the table and your blind structure.