With the nouveau driver my 6800gt's fan runs at full speed which is very loud. I talked to the developer of nvclock and he said that nouveau doesn't initialize certain registers that deal with voltages. Once these are set, nvclock should be able to control the fan speed. I'm not exactly sure what needs to be done, but thought I'd create to see if anyone had an easy solution.
Years later, I think we can close this bug. Fan management for nv40 has been released already.
No, its not fixed. Kernel 4.17.14 - fans just spin at 100% like inside the BIOS. They downt slow down. Waiting for fix for a looong time. This is just one of the bugreports: https://bugs.freedesktop.org/show_bug.cgi?id=102352