Upgrade to 8.04 and now Xgl is using 95% of CPU

[stan]

I just upgraded my laptop to 8.04, in preparation for going to 8.10, and
noticed it became very slow. I ran top and discovered that Xgl is now using
over 90%  of the cpu with virtually nothing going on, other than being logged
into a X (KDE) session). The Xorg startup log identifies the card as:

(--) PCI:*(1:5:0) ATI Technologies Inc RS485 [Radeon Xpress 1100 IGP] rev 0

And I am using the closed source graphics driver.

What should I check next to try to resolve this issue?

-- 
One of the main causes of the fall of the roman empire was that, lacking
zero, they had no way to indicate successful termination of their C
programs.