I upgraded to FF4 over the weekend. I hate the new UI. It seems like they changed stuff just to change stuff, without any reason for it. It took me forever to find the refresh button, and the first two things I had to do was revert back to menu mode and move the tabs to the bottom. I didn't think about moving the refresh button from the right of the location bar, but will probably do that when I get home.
My FF4 changes-
* re-arrange button bar (customize) Back/Forward - new tab - home - refresh/stop - address - (delete google search) - various add-on buttons
* FF3 look-alike theme (return to good looking buttons, basically)
* tabs on bottom (tabs adjacent to pages)
Can't think of what else I did just now, but after doing that much things were pretty much back to normal for me.
It wasn't hard to do these quick customizations and shouldn't stop anyone from enjoying FF4 vs. FF3.