I have been wondering the same thing. All I have read is that 2.1 will only have minor changes to fix some glitches. My main concerns are how to get the update (is it an OTA?) and if all my settings and apps need to be backed up somewhere beforehand.
I thought 2.1 was dealing with alot of the exchange issues since i didn't see any of those fixes in the 2.0.1 update (but they might have been). 2.1 will most likely have a few updated programs along with other minor fixes. Just look to see if you can find any details out about the HTC unit that had 2.1 on it, and see what it had. I know some of that stuff is just sense UI related stuff, but you might be able to tell some concrete stuff with it also.