Bad news first: you can't do (multi-card) multiseat on F10 using open-source drivers, and you won't be able to do it in F11 either. David Airlie's work on the Radeon driver is getting close, but there's still a crash-on-exit last time I checked.
Slightly good news: you can sometimes do multi-card multiseat on Nvidia hardware using the proprietary driver on F10/F11, if the phase of the moon is right. I have it working on a dual-PCIe system, but on another dual-PCIe+dual-PCI system (4 seats), I can only get three of the seats active at once.
Will may be better organize the multiseat as virtualazation of Desktops on the one X-server?
This way has more perspectives for stability and productivity ... less Processor, less memory, less time of second start the OpenOffice package.
This way need to patch the source of Xorg, and may be - some patches to HAL. This did allready by Userful Corp. (in Alberta) and worked very fine. But his sources is closed and his product "Desktop Multiplier" cost match. Some old patches of Userful X-server, HAL and others packages has the old site of Userful free wiki (may be live).
Good luck, Dmitry