To the best of NASA's knowledge (that they are releasing to the public anyway), the shuttle suffered no significant damage from falling foam. A few of the ceramic tiles on the bottom have small chips out of them, but that is perfectly normal on a shuttle mission.
Chaltab,
1. see above.
2. IF there is damage that could cause trouble on reentry, I think they would be willing to send up a second shuttle as a rescue vehicle, while the Discovery would be remote-piloted from the ground.
ChainsawAsh,
I'm simply going on what I heard. Perhaps there is a freon ban on NASA, given how much they would have to use for the shuttle. Maybe there never was a ban, but NASA was forced into the change by the Clinton administration, who was getting ideas from the environmentalists.
My point is, they made the change and I don't see a reason why they couldn't change back. They obviously used freon for 16 years (1981 to 1997) without serious repercussions, and since the shuttle is getting phased out, why not bring it back to remove the threat from foam?
Personally, I wish they hadn't scrapped the X-34 project (it was like a mini-shuttle). That design was far newer and was designed for this kind of thing (rescue/ trips to the space station).