There are strategic reasons to vote for Dean, Kerry, Clark, and Lieberman, depending on what the polls say.
If the objective is to Stop Edwards: vote for Dean if Edwards is closing in on 2nd, vote for Clark or Lieberman if Edwards can still be edged out for 3rd.
A vote for Kerry helps the Massachusetts liberal gain momentum to overcome his southern weakness and win the nomination.
A vote for Dean helps him stay in 2nd and sets up a Kerry-Dean race with Edwards being pushed to the side (hopefully). I don't think Dean can win the nomination at this point. I hope I'm wrong, but his negatives are HIGH.
A vote for Clark is potentially VERY useful. If Clark beats Edwards in NH, CLARK lays claim to the title of southern candidate and the two of them drag each other down and out. It would take the bloom off the rose and might prevent Edwards from winning SC, which would finish him.
A vote for Lieberman, who has been rising in the polls since his stellar performance in the debate, would be great if it gets him ahead of Edwards. A Kerry-Dean-Lieberman finish would suck the air out of an Edwards candidacy because the media would not be able to concentrate on more than three story lines, and Holy Joe would be the flavor of the day.