Version:           Unbekannt (using 4.1.3 (KDE 4.1.3) "release 55.2", KDE:KDE4:Factory:Desktop / openSUSE_11.0)
Compiler:          gcc
OS:                Linux (x86_64) release 2.6.25.18-0.2-default

2 Features are either broken or they are not broken but bad designed.

1. When I deactive compositing within a KDE4 session, one can clearly see that the desktop effects are not longer present, but the 3D Performance is lost - it could not regained for 3D apps, like a game
2. I can remember (bug 165237) that full-screen apps should not suffer from weak 3D performace when they are started within a KDE4 session with compositing activated - that is not realized.

In my opinion everybody can clearly see this behaviour with any 3D app - but to back up this statement I measured a lot of times, the 3D benchmark of the commercial game X2-The Threat. If anybody has  a better idea to measure this, let me know.

1. The average framerate of the game with my settings, is under IceWM/KDE4 without desktop effect between 34.4-34.6 fps.
2. On KDE4 with desktop effects enabeled it is between 14.4-14.7 fps (fullscreen app should not going through the compositing?!).
If I disable desktop effects and stay within the KDE4 session the framerate will not increase! Only when I leave the session and relogin, I get the higher (34.x fps) framerates. I assume login out will cause to restart the X-Server.

This behaviour is more than a showstopper, when I must always logout to get a 3D app working (there are others, not only games, think about GoogleEarth)