I went from a 2010 11" MBA to a 2012 15" rMBP and have no regrets. It goes with me about three days a week. Really love having so much power and a larger screen in something so light and portable.
Guys, I finally found myself genuinely wishing for a 13" rMBP over my 15".
I pulled/strained a muscle in my lower back/hip area after deadlifting 315 #. Carrying around a lighter backpack would definitely be more pleasing. So, while I'm a hunchback gimp, I find that shedding one pound in my backpack would be somewhat appreciated. I ate my own words. :-(