Although XFCE is rather short on creature comforts, it handles my dual output video card with separate X sessions on two monitors and doesn’t fall flat on its face with the right-hand monitor rotated into portrait mode. Some apps don’t maximize quite correctly, thinking the bottom is at 1200 (1080?) rather than 1680, but overall it works fine.
The XFCE version shipped with Xubuntu 8.10 is now backlevel, but you can fetch the latest & greatest from www.xfce.org. Add the repository (and corresponding public key), then do a normal upgrade.
You’ll also want to install/upgrade OpenOffice 3 from the PPA repository. Do the obvious search to find the most current links. There’s no need for the manual install hocus-pocus using a tarball from the OOo site.
You can’t have separate wallpaper on each virtual desktop, you must have the same number of desktops in each X session, and there are some other aggravations, but … no showstoppers so far.
Bottom line: It (pretty much) Just Works.
More on the system setup in a bit, as I get some useful results.