Alright. Bare with me here. It doesn't look like AIGLX is the problem. I think that may have been self inflicted with screwing around to get this working.
Upon rebooting everything still seems to be in order, but Beryl still crashes and reverts to Metacity immediately:
$ glxinfo | grep vendor
server glx vendor string: SGI
client glx vendor string: SGI
OpenGL vendor string: Tungsten Graphics, Inc.
Direct Rending is enabled as well:
~$ glxinfo | grep "direct rendering"
direct rendering: Yes
Then I open Beryl Manager and select Beryl and my window manager. Same thing happens... ie flicker. When I go back in to check my Window Manager, sure enough Metacity is selected again due to Beryl crashing.
I'm not sure if this helps, but I tried to select Compiz as well. That will stay open, but everything goes to hell. I loose the top name bar of all my windows and the right side of my top menu bar and task bar disappears. When I drag the windows and they go into their 3d effects, it leaves a trail that doesn't go away. The top menu bar locks too, so I can't right-clock the red gym icon to turn it off. I have to go in through Applications > System Tools > Beryl Manager.
Any input is appreciated.