The reason why I like forums a lot more than reddit (and why I don’t think they really compete) is that upvoting is actually an extremely flawed mechanic for fostering discussion. Not just that it breaks chronology, but because the easiest thing to consume is also the easiest thing to up vote. That reason among many is why reddit ‘conversations’ devolve into the crap that Jeff posted earlier.
Positive feedback is important, but not if it destroys the incentives for making in-depth conversation.