I had the 2.7/512/460 BTO ordered orginally, but cancelled it and bought the 2.7/512/455 in store because I didn't want to wait. It was nice but I felt like I wouldn't get used to the typing on the 15 inch because the trackpad felt so big and it has a big bottom chin. Just felt odd to type on, so I returned it for the 13 inch 3.1 i7/512 thinking the typing would be better. It was easier to type on for sure. I just kept thinking, though, that it would be too underpowered, and that I'd wanna upgrade again in 6 months or so. I ended up exchanging it for the same model I had, 15 inch 2.7/512/455. I brought it home, but didn't open it, because I convinced myself to go for the 2.9/1tb/460 that the stores have in stock. I want this to last quite a while without feeling like I need to upgrade so quickly. So, that's where I'm at now lol.
What I can say about my experience with the 15 inch 2.7/512/455 and the 13 inch 3.1/512:
-The screen was pretty good on the 15 inch. Whites were nice. Didn't notice much uniformity issues or odd coloring (something I'm always very susceptible to).
The screen on the 13 inch was pretty bad. The left side had a pink tint to it and the right side had a noticeable green tint.
-I did have the login graphic "glitch" when FileVault was on. I also got these weird artifacts once in a while in an open window. Well, right below the window actually. They looked like little white dots. A bunch of them off the bottom right corner of an app window. I guess the best I can explain it is, like glitter?
I didn't see the login glitch on the 13 inch, or that other graphic problem, but I didn't use it long.
-The keyboard on the 15 inch was ok. It did feel like the right side keys were a little louder and stiffer than the left, but I could have been imagining it.
The keyboard on the 13" was great.
-I was surprised at how cool the 15 inch stayed during any use. The 13 inch got a bit warmer.
-The typing experience on the 13 inch was "easier," for a lack of a better word.
-The 15" is incredibly light and portable for its size, and battery life was good.
Anyway, those are my observations so far. I didn't use either that much and haven't gotten around to setting up this newest one yet.
Hope this maybe helps.