I have been reading too many people here saying that portability is an issue with the 15", but the 13" is just right, I think that's sort of silly. If you can carry a 13" all day, you can carry a 15" all day. So what if it's a tiny bit heavier. Unless everybody here has 6% body fat, you are carrying around a lot more weight than the difference between the 13" and 15".

(Don't take that to serious now.)
With that out of the way, I do not think the 13" to be to small however. It does seem absurd that the 13" does not have a 1440x900 res, down right ridiculous as a matter of fact. I think it's Apples way of sort of forcing you into the 15".
I think that in retrospect, a lot of 2011 13" owners will be pining that they didn't just get the 15" for crisper display. All I can say is, if you haven't actually looked at the difference in quality between the 13", and the 15" first hand, and you already have a 13". Don't look at the 15" high res. It will make you feel bad.
I would pick screen res over a pound any day of the week.
Late 2011, new MBP 13" with 1440x900.