Of course weight isn't a POSITIVE thing, but it matters less if you're well built. A 120 ibs woman would probably suffer more than me from that extra 1.5 ibs.
I was actually dead set on a MBA 13 ultimate, but I realised I want a portable desktop more than an ultraportable. I think MBP 17 + iPad 2 gives me a lot more than just MBA 13, to be honest.
I genuinely feel like a broken record here, since I feel like 85% of my posts are defending the portability of a 17" laptop. I know a 98 lb girl with a 17" MBP like mine. Personally, I'm 130-135 and I've carried around a 17" laptop every day of university.
I use it literally everywhere. You guys must be going to sardine academy where you'll all packed into your lecture theatres because I've never seen a desk my computer wouldn't fit on. Get a knapsack built for your notebook and you'll never notice it's bigger.
Plus you'll get all the women with your larger screen.