I tried the Beta last night and it seemed really good; Gnome 3 is fast and I don't think it would take very long to learn some 'new ways of doing things'.
I'm not sure who's idea it was to remove the Reboot / Shutdown command from the user menu though - I spent ages trying to find it, only to discover through Google that you need to hold down Alt when mousing over the menu (I hate it when software makes you feel stupid).
The only thing that I really struggled with (and this isn't unique to Fedora 15 beta) is the font rendering - it was awful. I'm an Ubuntu user and find that the font rendering in Ubuntu is perfectly readable. It's the opposite in Fedora... which is a shame as it's the only thing that would stop me from switching from Ubuntu.