My first sexual experience was in my bedroom growing up, with my best friend. He was sleeping over and it was in the middle of the night. I never had sex with my wife at my mom's house, though.
I have had sex several times while staying at her parents' house. It's a quiet house and a quiet bed, and it's on a different floor from the other bedrooms. We tend to be pretty quiet, too, unless we're sure we're all alone.