Many people are playing with xorg 6.8.1 and the xcompmgr application. Unfortunately, it seems rare (currently) for the xcompmgr options to be documented. So here they are in full:
I tend to use “xcompmgr -cfC &”, but it’s up to you what you want to play with !
usage: xcompmgr [options]
-d display Specifies which display should be managed.
-r radius Specifies the blur radius for client-side shadows. (default 12)
-o opacity Specifies the translucency for client-side shadows. (default .75)
-l left-offset Specifies the left offset for client-side shadows. (default -15)
-t top-offset Specifies the top offset for clinet-side shadows. (default -15)
-I fade-in-step Specifies the opacity change between steps while fading in. (default 0.028)
-O fade-out-step Specifies the opacity change between steps while fading out. (default 0.03)
-D fade-delta-time Specifies the time between steps in a fade in milliseconds. (default 10)
-a Use automatic server-side compositing. Faster, but no special effects.
-c Draw client-side shadows with fuzzy edges.
-C Avoid drawing shadows on dock/panel windows.
-f Fade windows in/out when opening/closing.
-F Fade windows during opacity changes.
-n Normal client-side compositing with transparency support
-s Draw server-side shadows with sharp edges.
-S Enable synchronous operation (for debugging).