John Edwards is no Ralph Nader, as some here accuse.
Edwards will win a decent proportion of each state's delegates as long as he finishes above a 15% cutoff. Unlike Nader's chance of winning any electoral college votes, polling shows that Edwards is currently positioned to take 5-10% of delegates, and those numbers could easily improve.
If no candidate gets a majority of the delegates, then Edwards could play kingmaker by asking his delegates to vote for one of the others. Based on his recent statements, I suspect Edwards would throw his support to Obama in such a situation. Those of you who compare a vote for Edwards with a vote for Hillary are wrong--voting for Edwards is no wasted vote at this point since it will give him influence at the convention.
Edwards still has a legitimate shot at winning the nomination as well--elections are unpredictable, and frontrunners have been known to implode at times. Hillary and Obama could make significant gaffes, new information could come out that could turn voters off of one of them, or something else totally unexpected could happen. Maybe Edwards could even just get his message out and convince more people to vote for him--there's still time. In contrast, Nader had no chance whatsoever of winning.
Edwards leads all Republicans in general election polling, while Obama and Hillary both lose to McCain. Although I'm not sure how much weight to give to electability, Democratic voters should know that Obama and Hillary just don't match up well against McCain (I do agree with the polls on this).
Edwards wins among conservative Democrats despite having the most progressive message--this is a win-win situation: attract moderates and swing voters while still getting the most progressive candidate! See: http://www.blueoregon.com/...
Edwards polled at 27% in a recent NV poll, only 5% behind. The debate (tonight?) could push NV into the Edwards column, which would hopefully give him some momentum.
Edwards has the best economic positions, and as the economy sours people will pay more and more attention to this.