What are your opinions on screen size for non-retina MBPs? 13" seems like the perfect size for portability, but I find myself wishing I had a bigger screen. The larger 15" model is nice, but I don't know if it is worth the extra expense and decrease in portability. The 17" model WAS pretty awesome to look at, but I could see no reason someone would buy that if it wasn't going to sit on a desk most of the time. What are your thoughts? How do you use your 13/15/17?