I used to really want downvoting. Flagging really works much better. The stories that I would have ended up downvoting either don't belong here and get [dead]-ed, or they spawn a lot of fascinating conversation.

Fortunately, people haven't been doing a lot of gaming of the system yet. The biggest problem with upvoting only is that controversial posts garner the most votes (a thousand people love a subject and ten thousand people HATE it, so it gets a thousand upvotes and a TON of comments, even if most people disagree with the premise).