Edwards is evidently gaining quickly in Iowa, and today Iowa's largest paper endorsed him. Right now Dean leads Gephardt, there's a gap, and then Kerry is in third, with Edwards closing in.
I think this is bad for Dean, because Kerry's strategy would change from trying to overtake Gephardt, to fending off Edwards. This frees Gephardt up to focus on Dean.
The caucus math is really interesting in Iowa because voters show up, but if their first choice doesn't look like they'll reach 15% - on a precinct level - then they go to their next choice, until everyone is supporting someone who's over the 15% mark.
I think this might actually be an advantage to Dean because he's been campaigning over the entire state rather than focusing on particular regions.