I recently installed Beryl on my Kubuntu Feisty Fawn distribution and I run into two problems:

1) The window decorations were missing – here you need to add the line
Option “AddARGBGLXVisuals” “true”
to Section “Screen”.

2) My windows were all black and this is a bug in the NVidia driver which doesn’t seem to be fixed soon or at all – the problem is, that if you have a card with not much memory, like my NVidia Go 6200, windows content gets black since there is no memory available. There is a lengthy discussion about that here.
An easy fix for this problem is, right click on the red diamond (Beryl manager) in the system tray and choose “Advanced Beryl Options->Rendering Path->Copy”. This should have an effect on the performance but at least it works :). Thanks Nil.

More info can be found at these links:
An automatic easy solution for nearly (all) problems
Opening too many windows leaves some of them black