I didn't find out with our first, and it really did help me through labor and also when the baby was born it was so exciting seeing my partner scream "it's a boy" (he actually scared the crap out of me, he was so loud
)
I found out with my other 2 just because i was impatient, and well honestly the last 20 weeks of pregnancy were quite, i dunno, boring i guess.
I am now pregnant with #4 and we didn't find out, i am so excited and happy we didn't find out, it will give me more of an incentive to push him/her out, and i am really looking forward to hearing my partner yell out again!
I know people say they find out to be prepared, but instead of buying things we are putting money away weekly, and only buying a couple of basic things so when the baby is born we can go on a massive shopping spree as soon as i am out of hospital! also my partner is taking 1 month off work so in that month we will set up the nursery, as the baby will stay in our room for a while anyway!
Also the other reason i did not find out is when i found out with the other 2, i was still scared that the ultrasound person was wrong, it does happen! but i was worried that i went nuts on buying pink or blue and the baby would come out the opposite sex.