The main problem I find with a kid is that taking him anywhere is a pain in the ass. So, we go out when we can find a sitter, but that precludes being overly flexible. The overwhelming majority of our friends don't have kids, and the popular spots aren't kid friendly. Even other people's houses can prove to be a pain when you realize that people that don't have kids don't baby proof their house. And even restaurants during normal dining hours stopped being viable about six months ago because he's incapable of sitting still in a high chair for any period of time.
Now, friends still come over from time to time, but mainly just for the more laid back stuff that is available. Board game night? Sure, we can get people to come over. But just a general "hey, let's hit the town! I'm open to ideas!" kind of night? "How about my house? We'll have to keep it down after nine when the kid goes to bed, but other than that, it'll be fine! I'll get up an 18 pack!" It's... not the most compelling sell.