It is not inconceivable, but unlikely. The Celtics are as complete a team as there is in the NBA at this point, and they have few weaknesses.
I thought their guards were weak, but their backcourt is solid even with a young point in Rondo.
Garnett anchors the defense, and Pierce is unstoppable by one man. Ray Allen makes other teams pay for doubling KG and PP. Maybe if the Lakers get Bynum back they will have a shot, but even with him, the edge is clearly with Boston. I don't think Utah can handle the Celtics at this point.
No one in the East is good enough to stop Boston. Detroit isn't even making it out of the first round, meaning that the toughest opponent left for Boston is Orlando, who they won't see until the EC finals. They will draw LeBron in the 2nd round.