This is a subjective answer, intended to be just one opinion of many.
I've recently bought an Asus eeePC 1005PE and put Ubuntu Netbook Remix on it.
It was advertised as having 11hrs battery life.
I haven't put this to the test, but I must say I have been very impressed with the battery, as I didn't charge it for a week, only using an hour or two a day.
As for outdoor use, I used it in the car on a sunny day once, and didn't have too much of a problem. It's got an anti-reflect matt coating on the screen which helps.
There is currently a known problem with brightness on these netbooks, but there's also a workaround to fix brightness on the maximum level.
Hope it helps, comment here for more details if you want to know how to fix the brightness problem and I'll dig out the link.