Orpheus: most of the time, themes for linux window managers only change popup's looking and few other things.
In fact, window managers such as windowmaker or enlightenment are really powerfull, but you'll have to put your hands into the dust to be able to do something special...
but you can :)
The only missing part (as far as I know) is the ability to use application's icon automatically. Don't wish to use an iconed taskbar, for example; unless you manually define all icon the taskbar should use...