I'm running latest Ubuntu 12.04 beta on a Dell D420 laptop.
The fan is spinning almost constantly - even after turning the PC off, letting it cool down, and then turning it back on, the fan will turn on after some idle time. Not to mention any CPU work.
The CPU temps are normal, in range of 50-55 idle, and up to 70 with some load.
It wouldn't be an issue, but the same PC running Fedora, or Arch Linux, had a much more modest fan profile - the temps were managed while you seldom heard the fan.
To counter the problem, I currently use i8k tools, set manual temperature thresholds which seemed to have worked, but the i8kmon has a tendency to cycle the fan between lower and higher state within aboutin a second intervals - which is extremely annoying.
As far as I can tell I did not run any special software (beside laptop-mode-tools), or any additional kernel modules when running Arch Linux and I can't tell about Fedora.