Glad I'm not the only one with the mucked up scroll ball, that thing is very annoying. As far as form factor, I've seen a couple videos posted using it and it seems to work pretty well, but I agree, hands on to see if it is something that is going to work for you is always best option.
Macworld posted a
review of the Magic Mouse, if it does make have that scraping feeling I may not get it, I hate that sound and feeling when it happens to my other mice, ugh