I can vouch for dread's comment about the grey Innocase - I went through 3 of them trying to find one that wasn't impossible to remove. I finally gave up and went back to black (that's what I used on my 3G as well). I'm actually glad I went with black again because I like the finish better. The black is kind of a matte, marshmellow-type finish while the grey has a little more shine to it and it's not quite as soft. I don't know what it is about the grey ones but there is obviously an issue there so I would avoid it unless you really want a grey case.
As far as the Innocase scratching the bottom bezel, I assume he means that the bottom can get scratched because it's somewhat unprotected (not that the case itself scratches it). I could be wrong in my assumption though. Anyway, your bezel will get scratched either way. It's impossible to keep dust out of these cases so you're bound to get some scratches.