The Number Nine Revolution IV video card driver (i128) is broken for Ubuntu Intrepid based systems. There is a bug open to fix this at:

The short version is if you have this card and run startx you get a black screen. Press Ctrl-Alt-F1 to get back to tty1 and you see:
Xorg: symbol lookup error: /usr/lib/xorg/modules/drivers//i128_drv.so: undefined symbol: xf86usleep