ACL tear is tough to come back from, especially for basketball players, as opposed to other sports, like football. I tend to believe that, while Haith and co. have every intention of the starting 4 being Bowers' job to lose, they're probably pursuing a backup plan of some sort. That's probably why you're still hearing so much about Pollard and Goodman, even though it seems like there really aren't a lot of minutes available for another 3.
http://www.boston.com/news/health/blog/2008/09/recovery_from_a.html
"Weitzel, who works with the Boston Celtics, reconstructed the ACL in Celtics guard Tony Allen's left knee in January 2007. Allen missed the rest of the 2006-2007 season and struggled to come back last season. But Weitzel and other sports specialists said basketball players tend to beat up their knees more than football players and require longer rehabilitation times because of the daily pounding on the court and their quick lateral movements."
http://www.ihoops.com/training-room/strength-and-conditioning/What-to-Expect-After-a-Torn-ACL.htm?page=2
"Hand's knee injury was severe enough that she says she will never be the same.
"I'm a different player," Hand said. "I may not be as fast, but I think the mental aspect of the game, getting to watch for a year and gain that perspective, allows you to grow in different ways as a player. I think it makes you tougher, and it makes you take steps in different directions, and it maybe broadens your versatility as a player."
Both players stress that the recovery process from an ACL injury demands a level head. There will be good days and bad days--the key is to not get too high or too low."