the gnomeshell needs a "fullscreenize it all" feature!
it is really annoying, when you have to use fullscreen applications, that have to change your resolution, because your hardware is to slow( or for other reasons

)
so it would be useful if you could just start the application in a window and zoom into it, catching the mouse, blending out everything else and adjusting the mouse speed.
this way you could have any application in fullscreenmode without having to reset your resolution which is especially annoying if you have a smooth composited desktop and everything works great, but these fullscreen applications destroy everything

the compiz enhanced zoom plugin kinda does something like that, but its more of a hack (especially the mouse catching).
thats a feature im missing with all the composited desktops...
people seem to focus on all the shiny effects of the composited desktop, but they seem to ignore the window managing advances they bring...