The idea that hackathons can favor style over substance rings true with me. Sometimes people get unfairly screwed by a bad judging panel. This is particularly true when evaluating technical merit : I've literally seen judges swoon over cool looking Axure / Pidoco presentations.

However, it goes deeper than that as not even all developers (myself included) are always as good at evaluating technical merit as we think we are - particularly if the solution involves a lot of math.