Is "direct rendering enabled"?
If you have "direct rendering: yes", edit /var/log/dmesg and search for messages like this:
IRQ XX IRQF_DISABLED is not guaranteed on shared IRQs
Many users have reported problems with 2.6.29 and IRQF SHARED/DISABLED; in some cases, this problem affects nVidia cards too.
In my case, after I have switched to 2.6.29, I get the message (at boot):
IRQ 18 SAA7133: IRQF_DISABLED is not guaranteed on shared IRQs
and my DVB-T card does not work!