I just bought a new 13" MBP. I waited for the refresh and was a little disappointed in what was available, but in the end the 13" was the right choice.
I've owned a 15" before and I've had the 17" for the last 4 years or so. Although I really wanted to go with an i7 (I do graphic design, video editing, and use Pro Tools), my 2.16 C2C 17" handled all that stuff just great so I had to base my decision on what was the most important factor -- portability.
At first I thought the 13" display would just be too small for the work I do, but it actually turned out to be just fine. The resolution seems about right for the screen size, too. I absolutely hated my 17" MBP just because of the size -- it was virtually impossible to carry it anywhere. And although the 15" was a little better, it again came down to the compactness of the 13".
Since I plan on holding onto this laptop for at least another 4 or 5 years, my intention is to upgrade the ram and the HD to an SSD maybe a year from now once the prices have come down some more. That way, it will hopefully feel like I'm getting a substantial enough boost to feel like a new machine.