MoveOn members voted together to endorse a presidential candidate in the primary. That candidate is Barack Obama. Vote results Obama: 70.4% Clinton: 29.6% Press Release
I'm not sure how influential this really is because most of the people who would care about MoveOn are already so involved with politics they will probably be pretty well set with their decision already. That being said, it's a nice extra kick in the pants to get out the vote for Obama on Tuesday. Right now it's looking very possible that Obama & Clinton may pretty much split Super Tuesday, which means this battle may continue on for some time.
Organizationally, it is very important. MoveOn is the Democrat equivalent of the YAF. I think in the future, candidates will rely heavily on groups like this to enhance and market their campaigns, as old media dies out as a primary news source.