LXDE is a light weight desktop environment. It is not as full-feature as XFCE and some say it is just a bunch of program around Openbox and PCManfm. But actually there are more and more programs for LXDE and I think it has its place for light weight desktop environment.
LXDE under Ubuntu 9.04 is really very fast. If you are a minimalist and tired of Gnome and KDE and if even XFCE is too big for you, LXDE is worth a try. Apparently Ubuntu 9.04 does not come with the latest XFCE stuffs compared to XFCE's Sourceforge site.
Here is the screenshot with Lxlauncher which you may find similar things with some netbooks.