Under Linpus, the power consumption is displayed on screen when you click on the battery indicator. The numbers are in line with what you measure with your meter, suggesting 1) the onscreen data is accurate and 2) the power supply losses are minimal, say 20%.
Let's call the typical idle power consumption of the Aspire One 9W. Is this exceptionally low for a notebook? No.
My Thinkpad X31 idled at 8W. My T60 about 15W. (numbers corrected to compare with your meter readings)
Considering the small screen and considering the supposed power saving technology of the Atom CPU, it's a little disappointing that the X31 (Pentium M 1.3 Ghz, 12" cold cathode display, 20GB HDD, 512MB Ram) from 2003 consumes less power than Atom + SDD + 8.9" LED display from 2008.
If you are an optimist, you can think of it in a positive light: we can go to a 1.6Ghz CPU a much brighter display, and much more powerful graphics, and keep the consumption down to essentially the same level.
Still, I'd like to see idle consumption get down to about 5-6 watts, since that would mean we would see 4-5h use on the 3-cell battery and as a further benefit we could probably get rid of the fan...