Don't bet on it. Four times a team has been down 3-1 in a seven game post-season series and come back to win. Three times, that team was the Red Sox.
10/17 Update: Didn't I tell you? Down 7-0 in the middle of the 7th, the Sox come back to get four runs in the bottom of that inning (three of them thanks to Papi's bat), tie it in the 8th, and win in the 9th. I couldn't see them getting swept at Fenway. So, we go back to Florida, where the Rays will, I hope, prevail.