We've never found before birth because I choose to not do ultrasounds in pregnancy (unless my doctor before or midwife now would think something was amiss - then I'd do it in a heartbeat). I was extremely ill during my first pregnancy for about 36 of the 41+ weeks - so everyone and their brother told me it was a girl. I personally have always loved the heart rate as the gender predictor: over 140 = girl and under 140 = boy... and the stinker was EXACTLY 140 every single time. So when "she" was born with a penis... I was a little stunned =)
But his labor was also very long, and the pushing stage was an eternity (3.5 hours) - so for me, the finally knowing if he was an R or an M was totally worth it.
With my second, the pregnancy was completely different - so I knew (and was right) that it was a girl. This pregnancy is very much like that one, so I'm thinking another girl.
My best friend is due any day with her 3rd. They tried the first 2 to find out the sex, and both babies hid. She was frustrated, but what can you do? This time, the babe cooperated (girl). After the fact, she said she was really kind of disappointed that they found out - like most of the mystery was gone, and she didn't like that half the reveal (the other half being the looks of the baby) was already known. They think they're probably done with three, but she said that she would not try to find out the gender again if they have another one.