Minimalist action. Resource Conservation.
About 12 seconds from startx to desktop.
Fvwm2 configuration is not necessarily enjoyable, but it's a featureful kit. Versions 2.5+ are even better. To see amazing things done with fvwm, look here, or search oesf.org forums for Zumi's postings on fvwm. Brilliant stuff. Mine is about as basic-looking as it gets, but it's relatively easy to reconfigure and doesn't require any icon images. See the previous page for config files.
Links of interest: