Comment 3 for bug 877905

I believe I am experiencing the same problem, and it has been reported by another user on the Ubuntu forums:
http://ubuntuforums.org/showthread.php?t=1864567

The symptom is that no GLX application will run.

For example, compiz reports:
compiz (core) - Fatal: Root visual is not a GL visual
compiz (core) - Error: Failed to manage screen: 0
compiz (core) - Fatal: No manageable screens found on display :0.0

And, glxinfo reports:
X Error of failed request: BadLength (poly request too large or internal Xlib length error)
  Major opcode of failed request: 153 (GLX)
  Minor opcode of failed request: 17 (X_GLXVendorPrivateWithReply)
  Serial number of failed request: 17
  Current serial number in output stream: 17

However, there are no errors reported in my Xorg.0.log, including loading of GLX:
(II) AIGLX: enabled GLX_MESA_copy_sub_buffer
(II) AIGLX: enabled GLX_SGI_make_current_read
(II) AIGLX: enabled GLX_SGI_swap_control and GLX_MESA_swap_control
(II) AIGLX: GLX_EXT_texture_from_pixmap backed by buffer objects
(II) AIGLX: Loaded and initialized /usr/lib/dri/r200_dri.so
(II) GLX: Initialized DRI2 GL provider for screen 0

As reported in the Ubuntu forums thread, the two users there are running the 2.6.38-12 #51~lucid1-Ubuntu SMP kernel, one with pae and one generic.

The problem appears with both the intel i915 driver and radeon driver.

Reverting to the prior versions of xserver-common and xserver-xorg-core does restore GLX functionality, so it seems that the update is causing the problem.