> One cannot extrapolate, based on Xfce's performance on a high end machine, that it would be suitable for a low-resource environment;
Unlike Gnome, XFCE (at least in Xubuntu) doesn't seem to restart critical UI pieces when they crash, e.g. after user loads too large images in Gimp, system runs out of memory & OOM-kills random processes.
An older relative of mine lost his "Applications" panel menu because of this and it didn't come back even with reboot (maybe because of session saving?). He used only apps that had Desktop icons for few weeks until I had time to go and fix it...
So, although I like XFCE looks and functionality in general, currently I don't consider XFCE reliable on low-resource environments. Besides desktop, I've also noticed some of Xubuntu default apps have stability issue compared to their Gnome & KDE counterparts.
And in high-resource environments Xubuntu/XFCE apps are still lacking some features available on other desktops that I need on such machines (like reliable backup DVD burning) and its session handling seems to be having some issues with KDE4 apps (with which I replaced XFCE apps until switching to KDE completely because of these issues).
I want to like XFCE and I do, but to use it, it and its apps still need to mature a bit. Hopefully that happens soon after v4.8 is ready & in distros.