According to espn.com, Kevin Garnett could miss the entire playoffs.
Offensively, this is meaningless. Sure, Garnett is a good scorer and distributor, but Paul Pierce and Ray Allen can carry the team offensively with Leon Powe playing near the basket. Defensively, this is huge. With Kendrick Perkins, the Celtics had two outstanding defenders that complemented each other. With Superman Howard as a second round match-up, can the Celtics stop him? I just don't see it. While I don't see the Celtics stopping the Cavs in the Eastern Conference finals, you have to admit, the match-up does make for a fun seven-game series. Not only that, but with the Lakers wrapping up the Western Conference (sorry), you would have a potential Lakers and Celtics repeat OR a Kobe vs. LeBron death match. The possibility of Superman Howard and the Hedo Turkoglu's going against the Lake Show, even if it is a longshot, doesn't make for a fantastic finals.
Edit: John Hollinger wrote about this, but he used stats to back up his point.