Since MBAs are not upgradable, I was considering buying the top end 13'' MBA, 2.0GHz, 8GB RAM, 512GB SSD, which costs $2199. But then... if I get 13'' MBP, 2.5GHz, 4GB RAM, 500GB hard drive (so far $1199), and upgrade it with OWC 6G SSD 480GB ($600) and Crucial 4GB RAM ($26), then the total comes down to $1825. I would hate to add an extra 2 pounds in my backpack, but ~$375 difference is no small amount. Am I missing anything? Any advice?