I have a similar dilemma as the OP, looking for a new netbook and considering my options.
I currently have an MSI U123 with an N280 proc and 1 gig RAM. It has a 9 cell battery that gave me about 9 hours on idle, 6 hours playing video, which is great because I sometimes spend long hours away from a plug. It can play 720p h264 videos just fine in MPC-HC on Intel graphics, and even some 1080p videos like Big Buck Bunny. It plays my favorite classic games like SC, AoE, WCIII, Freelancer, Shogun: TW, SNES emulator, PS1 emulator, etc. A little more graphics power would be nice for smoother gameplay, but not critical for my purposes. I've had it for about two years, the battery is showing its age, and I've beat it up a bit from drops and scrapes (it is partly held together with duct tape). Been looking for a replacement.
As you can see, I'm pretty happy with the power of even a single-core Atom. What I'm looking for in a new netbook is a 10.1" or smaller that meets or exceeds the performance and battery life of my U123, but on a 6-cell battery (for size and weight), fanless if at all possible. Pineview didn't cut it, the C-50 didn't cut it, but maybe the new Cedar Trail N2600 can with 3.5w TDP. I'm eagerly looking forward to reviews when it comes out. However, I'm a bit jaded at Intel for the 5 months of delays, and the buggy PowerVR drivers which will likely give me problems on old games.
I'm looking long and hard at the C-60, which I had earlier discounted because of the poor battery life of its predecessor. I've read that this has improved. However, despite googling for information, I have not been able to quantify exactly where it stands in this regard.
So basically my question is, does anyone have some hard data on the power consumption of either an Acer AO522, the ASUS 1015B, or another C-60 ten-incher? For example I get a discharge rate of 9.1-9.5w on idle with brightness down and wifi off (ereader mode), 10.4-11w on a 480p h264 video, MPC-HC on XP in fullscreen. Diablo II gets up to around 14w, most browsing/youtube jumps between 11w and 13w.
I use BatteryBar to get this data, but it requires installation. If anyone is willing to help me gather some information, BatteryInfoView is free and requires no install. If you can't give hard data, I'd also appreciate any anecdotal information regarding battery life.