Do you have any numbers on this? Not that I demand proof, but I got interested in the actual savings and tried to google it, but didn't get any great results. The few hits I found indicated that the fan itself is quite the power hog, but changing the RPM from 2000 to 1200 shouldn't make a big difference, a watt or so maybe. Still counts, but less than I expected. Once we get to laptop processors that doesn't require fans, then the saving should be pretty significant - but that's still some time away
I doubt it's anywhere near 1 watt. I have several case fans that are far larger with far bigger motors than the one use in an MBA that use 2 watts at full tilt, there's no way 800 rpms in a fan that small will consume anywhere near 1 watt.