Republican Scott Brown, who trailed Democrat Coakley by over 30 points as recently as November, has steadily cut into that number. One recent poll showed Brown up by 1 point last week, though that poll seems to be the outlier. Brown still has to be considered a long shot.
There should be little doubt though, that even if Brown wins, the Democrats will tie up his confirmation with recounts and other legal delays to give them time to ram through the health care bill with the current majority.
Update: Seating Mass. Senate winner could be delayed. Secretary of State William Galvin in the past made a very specific exception to accelerate the seating of a Democrat in time to override a Bush veto. That isn't going to happen this time around - assuming, of course, that the outcome of the election is unfavorable to the Democrats.
"Massachusetts's top election official [Galvin] says it could take weeks to certify the results of the upcoming U.S. Senate special election."