Slashdot does this with moderation, and I have a few problems with it. Namely, I don't know which of the comments I'm currently reading are the top 5 comments that I'll read that day. Perhaps it's a slow news day in the morning, and I spend all of my moderation points on comments that are "good enough". Later in the evening something big breaks, and insightful comments abound everywhere - suddenly I have no points to spend on those comments.
I think that instead of creating an atmosphere of better comments, this will instead create a site that has higher rated comments in the morning, and is stale later in the evening.
I think that instead of creating an atmosphere of better comments, this will instead create a site that has higher rated comments in the morning, and is stale later in the evening.