Dude, the MB weighs 5 pounds--it's a brick (if it wasn't such a brick, I'd already own it). It's about the weight to me, too. And yes, two pounds is a big deal, especially when you're talking about something that weighs 40% less.
Please dont' go into percentages, as they are nearly meaningless in this context. One piece of paper is 50% the weight of two pieces of paper, but the difference is negligible. 5 lbs to 3 lbs is not a big deal. My old laptop, with its extended battery, was 8 pounds. My macbook is 5 pounds. I do not notice a significant difference. It really blows my mind that people are too burdened by 5 pounds.
Still, I haven't played with a MBA yet; perhaps the proof is in the holding (or using).