I use it, and like it. In fact one of my gripes about gnome is that the Debian fvwm folks decided to move to a new version that has some gnome integration. I value the gnome integration not at all, and I loathe the default behaviour on the new fvwm.
At some point I'll bit the bullet and upgrade at work, and probably switch window managers. But until the Gnome integration borked it, fvwm was a fine WM for my needs. (And my needs did not include modifying it significantly from what had been the Debian defaults.)
Cheers,
Ben