A couple of comment from my experience and skimming through here (didn't read everything, sorry).
GPS seems to have some issues for me. It can be slow to get a lock, even with some assistance from an app to clear and download data, and when it does, it's sometimes with less than 3-4 satellites. I think it always needed 3+ before. Not sure if there's a simple fix (unrooted, at least), but since I don't use location services much, I can probably deal with this, at least for now.
I have no silent option on my camera, which is definitely annoying, even more so when it makes a sound even though the phone is silenced. I thought that renaming the shutter sound files would work, and it probably will if you're rooted -- I can't rename the files on the stock ROM unrooted. If there's some other option that will work unrooted, please let me know. (OTOH, it looks like they put back a geotagging switch with the "GPS tag" option, which is good.)
As for moving apps to the SD card, yeah, calling it USB storage is kind of dumb, and I also noticed that it often took two taps to work, with the first one failing. However, it seemed to me that it only did that with apps I had previously installed to SD. If I installed an app I hadn't before, it took one tap to move. So my guess is that they changed something about how/where apps move to SD, the first click that fails for existing apps on the SD card does something to fix it so that the second click works, while apps that aren't on the SD card work right the first time. *shrug* This is an annoyance, but looks like it'll happen only once per app already on the SD, so it should basically go away eventually, I think.
Just a few things for now. I'll probably check back for other issues and hopefully fixes for them. I'd prefer things I can do unrooted, but since Gingerbread's probably the last official OS update the Epic will get, I'm more inclined to root now to get what I need. BTW as an aside, pointers for good, easy-to-follow, beginner root/ROM guides would be appreciated; I'm generally not bad with technical stuff, but have never rooted my phone before. Thanks.