I don't have a GTX-5x series card, but, I'm running UB-11.04-Server with NV 280.13 driver, Cuda 3.xx 32bit Tookit, 3.xx Wrapper on (8) 9800/8800 cards, and all seems well for the time being.
For upgrading, I just ran: NVIDIA-Linux-x86_64-256.35.run --update and let it DL the new driver during install, then installed the Cuda 3.xx toolkit & followed the rest of the guide. Have not seen any adverse affects yet.
2x - Q6600 1 with 2x 9800GT's / 1 with 2x 8800GTS G92 512's UB-8.04 CLI Only
2x - AMD 9850 1 with 3x 9800 GT's / 1 with 1x 9800 GT's UB-8.04 CLI Only
1x - QX9770 GTX-280 WinDoze Vista 64