What do you do with fvwm that you can't do with gnome? I used fvwm for quite a few years from about 15 years ago, and i can't say i miss it.
Well, I for one can run it on my hopelessly antiquated computer
Maybe I don't have enough windows open at a time to really make it worthwhile, but the few times I played with them I always just ended up losing my windows and hunting through each desktop to find them. I think Alt+Tab / Win+Tab works fine (even better on Vista/Win7 with more detailed previews).
Remember where you start your apps. I have my virtual desktops arranged in two 3x2 grids, one labeled Personal, the other Work. Numpad 8 and 5 switching between the two. Numpad 7, 9, 4, 6, 1, 3 are bound to each screen within that section. Now on Personal, I will always run mutt on 7, Firefox on 9. On Work, I will always have Emacs in 9, xpdf in 7, figure editor in 6, spare terminal in 1, Matlab in 3, etc, and finding the right program is just a matter of hitting the corresponding Numpad key. This works extremely well for me.
Right-click any shortcut in the Start Menu or on the Desktop, go to Shortcut tab and type what you want in the Shortcut box. This works anywhere in Windows. In Vista and Win7 you have even more choices, for example, the Windows key + numbers opens the programs in your QuickLaunch in order (Win+1 opens the first shortcut, Win+2 the second, etc).
I'm guessing GP meant keyboard shortcuts used for other things, in addition to opening programs. Especially FVWM has huge possibilities here, and some people are quite into that. I obviously have quite a few myself (primarily window operations -- maximize, move windows between workspaces, etc -- The 'Windows' key actually comes in quite handy here).
My personal #1 annoyance with Windows, though, is that there is no easy way (at least that I know of) my modify the keyboard layout. I live in Denmark, but the Danish keyboard layout was really designed by someone with their head way up their ass (AltGr+7/0 to get curly braces? Bah). I personally find the UK layout rather good in many ways, but even using that as a base layout still leaves me with some serious xmodmap work to be done before I can use a system.