Dean had a mixture of anti-war support and college age people, essentially the far left. Both groups don't win elections, in part because the majority of the left is always afraid to ally with them for fear of "electibility" issues. So Dean was left with an unstable group of supporters and his numbers reflected that, especially in places like Iowa where the politics aren't exactly hardcore liberal; who knows, if the first primary was held in NY or California things could have been different for him.
The early primaries are really going to kill Obama this race imo. If he loses badly, he can kiss his chances of expanding his black support goodbye; blacks aren't going to move to Obama in any large numbers until it seems like he can win. Also, this undeserved Kennedy-esque aura Obama has will die if, after all the hype and "hope", he can't compel the new generation to stand up and vote. Kennedy inspired people, especially the younger people of that time who are in their 50s and 60s today and still haven't gotten over his death. I may not particularly like the Kennedy kool-aid but it's useless to argue with history. These people are looking at Obama curiously, wondering whether he's truly "the one" so to speak.