I'm using a Asus W3V as my only computer and in my experience it's a perfect hybrid between a main purpose/portable/powerhouse gaming laptop. I get 4 hours of battery life and it's not noticably heavy at all when lugged around and when I get home I can play any game I'd like.
It runs GTA San Andreas & BF2 perfectly.
But if I were you I'd get the upgraded Asus W3J which is the same laptop but with Intel Dual Core & ATI X1600 GFX!
It's a nicly sized 14" WXGA laptop that weighs only 2.2 kg(4.9lbs?)
EDIT: The W3J will be available late march/early april.