Well, first off, congratulations to the four of you! Life's about to get even more interesting...
Now, for the sex thing... we didn't find out with either of our kids. Partially, I think it was to pi$$ my parents off, since my mom really, really, REALLY wanted to know. I also like the surprise, and the moment of truth (dear, it's a...)
Hmmm... as I think back, I think we did find out with our second child. I remember singing songs to Alaina about her impending brother.
Personally, I prefer the surprise factor. Realistically, though, I don't think it really matters. What matters is that your new child will be healthy and strong... whether it's a boy, a girl, or not alone