Re: to the 5800 ultra users: fan coming on while in 2-D
All of the drivers that I've used for the 5800 will occasionally run the cooling fan in 2D mode. These include v43.45, 43.51, 44.03, 45.23, 52.16, 53.03, and 56.72 that I have tested personally on this card. And I agree- it's not always temperature related as with the latest driver (56.72) the fan will spin-up briefly after the monitor resumes from a 'power-down' state after being left idle for a long period. Also does run when playing certain .MPEG files, but not all (?). Does NOT run playing DVDs thankfully...
To sum it up, I have found that every driver released for this card exhibits this behavior, although there are subtle differences. I can't recall which driver actually 'minimized' this effect, but I believe the fan is run for a reason, so it's best tolerated not avoided. In fact, certain high-bandwidth .MPEG files will actually 'crash' the TV-out when the fan fails to start. I have repeated this many times with several different drivers. It is somewhat annoying only because the fan itself is somewhat annoying, but we all knew that when we purchased the card, right?