This post is way outdated now, but given the low activity at the Dad's forum, bumping doesn't seem like such an egregious sin.
I'm just like the OP's husband. I have trouble wanting to get out and do groupy social things. I was an only child and my own parents didn't play with me much (parents sometimes "give up" on boys after awhile and leave them alone, while giving more attention to girls and their feelings--it's a socialization thing), so I spent a lot of time doing things by myself and when the weekend rolls along I need time away from people in general. It's not social anxiety, I don't become ill talking with others and I am a good conversationalist, but I usually prefer some "me" time on the weekends.
Anyone else like this? I would guess that there are more Dad's like this than not, though there are many social extrovert dad's out there.