In a few words, there's low performance with rather good hardware.

Hardware: Intel Core i7 2630QM, AMD Radeon HD 6850M (important point is that glxgears and fgl_glxgears shows just about 1000 and 500 frames per second, respectively - as on ancient Radeon 9600 and so on)
OS: Gentoo x64
Video driver: fglrx 8.93.4 (catalyst 12.1)
KDE 4.8

Xorg config is default generated by aticonfig --initial. Device section:

Code: Select all

  Section "Device"
     Identifier  "aticonfig-Device[0]-0"
     Driver      "fglrx"
     BusID       "PCI:1:0:0"
  EndSection

Cover switch is used as window switching effect.
KDE theme is oxygen-transparent (but there's the same with default oxygen).
Disabling blur and some other effects makes no difference, but applications launch faster when disabling all effects.
If it does matter, preload and prelink are used.

All animations were just wonderful on clean install (Gentoo, I mean) with KDE (4.7.3 at the time) and fglrx (Catalyst 11.11 at the time, but there's not a 12.1 problem)

Cover switch is now smooth only when switching to the same window which has already have focus, while simple window list scrolling is smooth as it should.
Application launcher, krunner, etc. slide smoothly only if all windows are minimized. Generally, all effects are slower (or sometimes even frankly slow - btw, sorry for my poor English) with open windows (proportionally to open windows, which aren't minimized, count). With no open windows effects are smooth.