Having gone from a non-r 13" MBP to a non-r 15" MBP with the higher-res screen, I quite enjoy the extra elbow room I have. My main purposes are pretty specific: editing photos in remote locations and DJing. For both of them, extra pixels really make a difference. As a bonus, the 15" has a much (much) better video card and I can actually do some gaming when I'm not at my desk. I've recently taken to Driver: San Francisco and Borderlands 2. The old 13" didn't have a prayer of running either of them.
...of course, none of the above really pertains to the