Comment 61 for bug 199960

The test program does detect Xgl.

smoku@wing:~$ gcc xorg_xgl_info.c -lX11 -lXv -lXrandr -o xorg_xgl_info
smoku@wing:~$ ./xorg_xgl_info
Xgl: yes
Xrandr: 1.2

And those discouraging Xgl should _really_ read http://lists.freedesktop.org/archives/xorg/2006-February/013306.html