I was having a play with the XGL LiveCD yesterday. It has the same shortcut keys as my FVWM setup to switch between screens (Ctrl-Alt-Arrow), which is nice.
It also has a “Take currently active window with you when switching to a new screen” option, which struck me as a useful command: I’ve always used a menu to move windows to a new screen, and then followed the window with the appropriate shortcut.
I’d far rather be able to use a shortcut key combo to go to the new screen & take the window with me. I’m sure FVWM can do it, but I can’t work out how to tell it to.