Aren't atom cpus speedstep enabled? I haven't checked on linux but they're always running @ 1,60 ghz. Shouldn't it decrease a bit when there's no work for the cpu?
From 100% to 8%, 3 cells battery, ssd laptop and processor running at 800MHz, 2 hours 20 minutes.
To make your processor run at 1.6GHz at all times (AC supply connected) just choose Always On on the energy profiles in winxp. I don't know about linux.
In 3 days, a completely turned off laptop discharges by 6%