1. All applications work flawlessly with Compiz..

2. Compiz can never replace KDE and Gnome , as it uses DE's as its base to provide desktop effects..

3.Compiz is improving in stability and performance and plugins but its not as fast developing as DE's..

4. Forget about that can a 256Mb Ram based PC can even install VISTA or Mac OSX ? Running effects is a different matter.