Since I first posted I've given Sidux, Fedora and Debian Xfce versions a decent testing on an extra hard drive. All three ran zippier than Xubuntu (and maybe even a hair zipper than our fave distro, too
). All three were easy enough to get the "extra" things working that some might need (nvidia drivers, codecs etc), all it takes is a little poking around in the forums/wikis.
Sidux was really interesting, a "stabilized" version of Debian Sid (unstable). There is a lot to learn to get it set up how you want it, but there are scripts that will help (smxi). It seems like a good distro for a tinkerer. FWIW, the Sidux forums heavily favor the KDE version, but there is a dedicated live CD for Xfce that works well. The live CD has a handy list of "cheat codes" which is helpful for getting it up and running with your hardware. The installer was easy to use and unique (to me).
Debian Xfce was OK but for some reason it didn't do anything special for me. The packages were oooold. I gather you can change the "stable" to "testing" but at that point it looked like Sidux would be more fun to learn. I could not find a live CD for Debian Xfce (only the main Debian releases seemed to have live versions) but the installer booted up fine.
The real surprise for me was the pre-release Fedora 11 Xfce "spin". It was my first go-round with an RPM distro. The live CD booted off my nvidia card without any input from me, and I could even turn on window compositing running from the CD. The install was easy and the apps were right up my alley. Thunderbird 3 and Firefox 3.5 were already loaded and I felt like I was living in the future. I think I might keep playing with this one for a few days.
I think Xfce and LXDE are truly neglected middle ground DEs and I hope they get more exposure. Especially the Xfce 4.6 release. Easy to use and light is a great combination. Frankly, I cannot figure out what I can't do in Xfce that I could be doing in Gnome...
Thanks for the Sam info. More, more!