As part of the process of building the separate MythTV box (as seen in my last few posts), I no longer needed the VDPAU acceleration for TV playback on my main PC. I also wanted to see if the suspend and hibernate functionality worked with the open source nvidia drivers (nouveau), as opposed to the proprietary binary ones. Booting the system with an Ubuntu live CD, which uses the nouveau drivers by default, let me suspend the computer and resume correctly - something it did not do with nvidia's binary drivers.
So under System -> Administration -> Additional Drivers, I disabled the proprietary drivers, which re-installed the nouveau driver. Rebooting, the screen came back up, but only one of them (I have two), and at the wrong resolution. The cause of this was a fix I had applied earlier to make the boot screen look right with the Nvidia drivers, as described at the end of this earlier post. Once I removed the extra text from the grub boot command, everything worked fine. Suspend and hibernate both worked, although I found hibernate to be a little pointless - it took about the same length of time as a normal boot.
The only downside was the compiz desktop effects no longer worked, although I believe if you use a more current version of the nouveau drivers it may do so. 3D performance is nowhere near what the binary drivers provide either, but that isn't so much of an issue since I dual boot with windows. Games can be played there.