We have a couple parent friends, but we usually hang out with them one-on-one... as in, our kids all play together while the four adults chat and hang out.
It's pretty rare that we get together with our friends in larger groups... although Bee was in some mommy groups early on that all got together like that. The social dynamics of larger groups can be tricky though.
If you hang out with parent friends, do you hang out one on one... or in groups?