We didnt' find out with DD1, mainly because it just wasn't common practice then. We did with DD2 mainly because DD1 had her heart set on a girl and I wanted to prepare her if it wasn't a girl. I found it to be a really special time for bonding. It was wonderful both ways. THird time we havent' found out and I am finding that Im not so interested in the pregnancy. With DD2 I shopped and bought things for her, but this time I have no desire as I dont know who Im carrying.
As for people giving their opinion, I truly believe people will say what they did. So if they didnt' get the opportunity to find out, they will have a go at you for finding out. Everyone wants to be right. I just take it with a grain of salt. People want to know that their choice was valid, and if you're doing something different, it may say to them they were wrong. JMO, but I have thought about it alot as I have an inlaw that is sooooo like that!!
Good luck with finding out, I think it's one of the most exciting days EVER and I can't say it was any less exciting finding out at 20 weeks than it was at birth. Both just as special xoxoxo