Well you knew he wasn't going to endorse Edwards. Anyhow, check out this bizarre analysis from Politico:
"Kerry, who had contemplated another run of his own this year, remains one of the Democratic Party's most popular figures, and gives Obama a big boost as he is trying to regain his momentum after finishing second to Sen. Hillary Rodham Clinton (D-N.Y.) in the New Hampshire primary on Tuesday."
My impression was that Kerry wasn't particularly popular within the Democratic Party. In fact, I sort of remember folks on the left telling him to shut up during the mid-term elections. I don't think this harms Obama in the least, it has to be viewed as a net positive, but not necesarily a watershed moment.