I didn't find out with my first and wasn't planning on finding out with my second but the day we had the the 3D scan she had her head turned (was posteria bub) and DH saw I was feeling disappointed because we wanted those pics of her face and she wouldn't face the right way so he suggested finding out the sex so we'd have something to be happy about as the pics were all of the back of her head, lol.
I'd always find out the sex in the future. Definitely didn't regret it at all. But having a "surprise" at the birth with DS wasn't a regret, either. I don't know why anyone would "regret" finding out or not finding out, unless they were disappointed with the sex that was revealed?