I have the 15" now, but it's a little too heavy for me for regular mobile use.
Meh, I've tested one. Weight is good for me. I had a 1.8Kg 13'' laptop, and I currently own a 15'' that weights 2.5kg, so the Retina 15's 2.0Kg are no problem. If I wanted lighter I'd go for the 13'' and then build a desktop PC.