I recently (2 weeks ago) went for the 13 inch because I wanted to get in as cheaply as possible (and still be able to upgrade the RAM/HDD myself). I was worried about the 13.3" screen, but the touchpad gestures and easy desktop switching (3-finger swipe) make it VERY usable even at that size. And it's 1280x800, which is a pretty standard resolution for slightly larger screens on other types of laptops (higher DPI is always nice), anyway (GF's 15" Toshiba is 1280x800). If I get really desperate for screen real-estate, I also picked up a mini DP-> HDMI (and another for VGA), so I can attach another monitor (when one is available).
My decision was MOSTLY based on price, but I'm not dissatisfied with the size of the screen.