Unfortunately it doesn't seem to fix the issue on the Sabertooth 990FX, either.
I use Sabertooth 990FX (BIOS 1102), AMD FX 6100, GeForce GTX 550 Ti, GeForce 9800GT with 16GB RAM on Fedora 16 64bit (3.3.0-8 kernel) with the NVIDIA kernel module version 295.33. When IOMMU is activated in the BIOS - regardless of IOMMU reserved memory settings or memory remapping settings - I get the same errors in dmesg as Deanjo on page 1 and no X. When I use the nouveau module, I don't get these problems but 3D acceleration is painfully slow and makes the PC unsuitable for running as a Xen virtualized multi-OS, multi-user system (which is what I built it for). So that project's been on hiatus waiting for a patch or fix.
I've tried various xorg.conf settings, several distros and a horde of different kernel and BIOS configurations but nothing seems to help with this problem, aside from IOMMU - if IOMMU is on, the nvidia module doesn't work and if it's off, it does.
That said, here's some of the interesting topics on other forums from people who've had similar issues:
A Gentoo user provides very detailed information and seems to resolve his issue without disabling IOMMU
Kernel.org bug submission with a suggestion from an AMD IOMMU kernel developer to NVIDIA.
A user on this forum. 'Fix' is to disable IOMMU.
A user on the NVIDIA forums seems to solve a related issue on a 32bit kernel by disabling memory hole remapping.
Same issue as above with users on the Gentoo forums.
A user on TweakTown had similar problems with a 2.6.x kernel and a Gigabyte motherboard.
A Debian bug submission.
Nouveau had similar (?) problems in the past.
...which were fixed.
Hopefully these will help NVIDIA isolate and remedy the bug or advise us as to any configuration or hardware conflicts.