I didn't want to find out with DD. I desperately wanted a girl, but I knew if I found out it was a boy I would harbour feelings of disappointment. And I didn't want that for even a second. She was my first and I had no idea about the reality of gender disappointment.
With DS I was following the same path, didn't want to know to stave off the feeling of disappointment (wanted another girl), but I found out by accident. I will always wish I hadn't. More though because of the surprise at the birth was lost. I was so stunned to find that (for me). I had known a long time but the feelings for me didn't start until much later after birth, so knowing or not didn't make any difference.

I don't think there is an answer....I'm pondering it again with #3.