Just got the extended battery yesterday so can't speak to the life yet, but a couple of observations on the fit and case issue:
Appearance: As has been said by others, the extended battery and cover fit like they should have always been there. The phone is now only slightly thicker; uniform instead of a bulge at the top. I actually think it is easier to hold now. Given how well it fits and looks, I'm a little annoyed that Verizon/Motorola ships the phone with an inadequate battery when the bigger one seems like such a natural fit.
Case: I bought the Verizon black rubberized case before I had the battery. It actually still fits even with the extended battery (a testament to how little the extended battery changes the dimensions). Even with the original battery the case had an issue with the top power/unlock button being a little tough to hit. It isn't any better with the case on the extended battery, but it isn't any worse.
I'll report back on battery performance once I've let it run its course.