I'm not sure.
On the one hand, I soooo want a daughter (this isn't a one-boy-one-girl thing, I have always wanted a daughter) and I feel so eager to find out! I also want to know if I can buy a few frilly things. I'm not huge on dressing girls all in pink and boys all in blue, but I have NOTHING girlie at all, it's all either boyish or neutral, and it would be nice to have something floral.
On the other hand, I really liked getting the whole surprise at the end. I know, it's a surprise whenever you find out because you didn't know before then, but somehow it's a bigger, more dramatic, more naturalistic this-is-how-the-generations-have-done-it surprise when you find out at the baby's birth.
So I think I'm leaning toward not finding out. I'll probably buy some girlie things anyway and use them as gifts or put away in the hopes of having a girl someday if we have another son. I'll take something neutral to the hospital, or one boyish and one frou-frou girlish outfit.