At first i bought an Acer 6292: very powerful machine for being a 12", but i didn't tolerate the heat on the wrist rest area.
So i sold it after few days to a friend, and bought an HP-Compaq 2510p (second hand for 700€).
It's somewhat slow, but very portable and it sports an excellent keyboard.
Both machines can work on the net for 5 hours (my experience).