Yesterday was xfce 4.8 test day, so i decided to give it a try. just did a 'yum install @xfce' at my F15 Alpha TC2 based install.It work very well and was much more stable than gnome3 there is a little buggy at the moment.
gdm dont support starting anything else gmone3 at the moment (Hope they fix that soon) so i had to boot in runlevel 3 and use startxfce4 to get it running.
The default interface is not the most sexy looking in the world, but with a little tweaking it go beaten into shape.
I have done the following:
Enable composition in the widow manager setup.
Added shadows and make windows borders transparent.
Removed the bottom panel and installed docky. (yum install docky)
Got a new theme from here. (put it into ~/.themes)
Remove some stuff from the top bar and remove the frame around the notification area. (you can use expanded blank separator to center the clock widget and put the notification to the right)