I've been through this a few times, went from 17" and decided it was way to big and heavy so never took it with me and then switching to netbooks in 12" form factor which I decided were very portable but not that great to work on. Then switched to 13" which just ended up seeming like a bigger heavier netbook to me then switched to Sony Vaio Z 13" which was the ultimate in portabilty and power but in the end the screen real estate was just not enough to do any serious work on. So I ordered a 15" MBP and without a doubt it is the perfect size for me as far as portablity/power/screen real estate go. I really love that Z it is quite a marvel how much power it has in such a small package but unfortunately for my old tired eyes the MBP 15" is a much better option, I will be purchasing 15" from now on as IMO it is the perfect size for portabilty/power and screen real estate. Haven't tried a 14" that might be nice as well but there is no macbook in 14" and reason I switched to macbook was for the thinness it is about as portable as you can possibly get with a 14"-15" form factor latop.