*I love that DVing costs reputation b/c it keeps the trolls at bay*  
Trolling isn't a problem on SO, is it?

*but I also get really annoyed when I see a post with 2 answers, one of which is obviously incorrect, that both have a score of 0. I would prefer that the bad answer have a -1!*  
Why won't you give the correct answer +1 instead?

Personally, I think that comment explaining why answer is bad will help community a lot more than downvote. A lot, lot more. It will help 'answerer' to realize his mistake instead of alienating him for no apparent reason (the reason why answer is bad may not be obvious to everybody).

**edit**  
**Richard JP Le Guen** has really summed up my philosophy about downvoting: "*Reward the good; ignore the bad and only punish the terrible.*"