I am consistently getting 4:30 when setting display on third from lowest setting. I get more like 3:30 when turned up. It actually is an improvement over my last MBA which was a rev B 1.86 with SSD.
I do a lot of writing (typing), and I have gotten used to turning the display brightness way down for that, but when I am doing other things like Internet, video and etc I get around an hour less. I use a 3G card also, and it does drain I am sure.
BTW, what 3G service do you use? I use AT&T, and it's seriously fast and very nice to always have Internet access without worrying about "hot spots." Definitely worth the $60 per month... BUT, I wish I could just share (tether) my iPhone 3G connection which I pay $30 for the data for it. I would happily pay an extra $30 for tethering and save $30 per month, but I wonder what that would do to the iPhone??? Would it wear out sooner?