Re: nvidia driver quality decrease?
Unfortunately the cornerstone of a smooth desktop experience is the video driver... and that is always the biggest point of contention in Linux.
Your fan problem definitely sounds like a bug somewhere... but unfortunately it's probably not exclusive to the nvidia driver, especially since it first appeared when you upgraded to 12.04. And I only say that because there are other people with the driver and video card that don't experience the problem, e.g., the nvidia devs who are unable to reproduce the issue.
I almost feel like I have fewer problems with my Hackintosh than I do Linux.