Undeterred by my prior failure in prognostication, here is a bold prediction:
Two years from now people will think that Howard Dean's yelp cost him the nomination. In fact, he had probably lost it earlier. Let's remember, he got flattened in the Iowa Caucuses before the "Eeeeeyyyyyaaaaaaahhhh!" ever came out of his mouth.
This is something that Bill James, the baseball analyst, has commented about in the past. Over time, events that were memorable tend to be remembered as events that were significant. I don't think Dean's yelp was all that significant. It confirmed he was swirling around the political toilet, but the voters in Iowa had already pushed the handle.