To repeat: SXGA+ = 1400x1050, UXGA=1600x1200
I have an SXGA+ resolution laptop at the moment with a 15" display (a Dell I5000). IMO, the resolution and screen size is just about perfect. The writing on web pages is small, but not too small.
UXGA is only 14% more pixels in each direction. I've seen a friend's UXGA and the fonts start to look small. It is still readable though, but if you have poor eyesight, you would not want this option. Otherwise, you would probably get used to it.
For old games, UXGA is the more supported resolution. I never saw many that offered SXGA+, whereas UXGA was quite common. (However, I haven't bought any in ages, so this could be wrong). New games probably support both resolutions, however you are unlikely to be able to run the likes of Doom III at either resolution with the 9600 pro chip and get a decent frame rate. In this case, UXGA scores again as you can select 800x600, which is exactly half the native resolution of UXGA and it should zip along.
I have gone for the UXGA screen, but I have a feeling I will probably miss the SXGA+ resolution; as I said, it is just about right.