The polls in Iowa in the last few days before the caucus showed Kerry and Edwards surging up and Dean and Gephardt falling back. This momentum clearly continued and was exacerbated by the caucus system ... if you don't have quite enough supporters to reach the 15% threshhold, you go to another candidate's group and get 0 delegates from that precinct.
If there were widespread cases of people actually ending up at the wrong place for their caucus, this would have at least been reported somewhere by a reputable news organization. Are there some dirty tactics in elections? Sure, but if they're really significant and widespread, they're going to at least get SOME legitimate coverage.

I'm sorry, but this robo-calling issue is just an excuse that has found an eager audience. Many people who first liked Dean were not entirely sold on him and the scrutiny of being the front-runner cost him dearly -- I know, because I went to the caucuses undecided between Dean and Edwards, and ended up going with Edwards. I just felt Dean had reversed himself and revised his positions too many times, and the GOP would eat him alive.