How to have a fulfilling social life as an academic
The special thing for you coming out of (what seems) a pretty demanding grad school time is that being a postdoc is not so special at all. In most ways, being a postdoc is not unlike any other time-demanding job. You come to work in the morning, spend most of your day there, and, in the evening (whenever that is, time-wise), you will more often than not go back to your home and stay there to relax a bit. You bond with your co-workers, but usually more in an "acquaintance" than in a "friends-for-life" way.
Anyway, it seems to me that you are thinking that you can only hang out with people on your academic "level". This has never been my personal experience at all. In all my work places, grad students often hang out privately with the postdocs that they work with, and many of the younger faculty staff often join in for ad-hoc parties as well. I guess it is all a question of how you want to appear towards your junior work mates. There are people that see fit to construct an image of aloofness towards their students, and others like to mingle. Nothing wrong with either, of course, as long as your work relationship stays reasonably professional.
My limited experience of postdoc life is that there can be plenty of camaraderie; it just depends. I certainly hung out with the other postdocs, got invited to their homes, met their families, at least to a limited extent. So, yes, there is some bonding
In some ways it is not that different from grad student life. While a postdoc is more like a regular job, and I think everyone likes the fact that you are not as dirt poor as a grad student, you also spend time commiserating with each other about the crappiness of the job and worrying about the job market. Depending on who you are working for, you may also spend time complaining about the boss (or bosses). Since postdocs on average last a shorter time, one is liable to see people come and go even more frequently than in grad school, which does make it more difficult to have longer term friendships.
Having said all this, it is probably a good idea to find other people besides those you work with to hang out with. This is true of any job, of course. One suggestion - go dancing!
Great answers here. Looks like all the answers are US-based (from what little I know about US academia)... so let me add how it looks like from a perspective of a European research lab.
Note that I say research lab because the association to the Uni is really very loose, mostly meaning rarely who is attending classes at the uni. It is a fairly big lab, and very transitional (not many people stay long). It comprises people that are:
- PhD students (some of whom have a class or two to TA) staying for 3-4 years
- Master interns (staying for 4-6 months) and PhD exchanges (staying up to at most a year)
- postdocs (staying for a year, to at most two)
- engineers (staying for anywhere between 6 months and 2 years)
- permanent positions (researchers + professors)
None of us have classes together, there is many areas of computer science in the lab so most of us don't even share deadlines. As I mentioned, it's a transition place where a lot of people come and go very fast. Still the social life is quite fine. We meet on smoke breaks, coffee breaks, through officemates, through friends, ex uni buddies, cause somebody hears the accent of his nationality... I have a pretty active social life, at any point the group of friends I go out with is between 5 and 10 people. Some postdocs, some PhD students (both in their last years and just starting), an odd Master student on an internship, some engineers. Some people have teams that are much more involved, so they have team-nights-out, and I've heard of young supervisors inviting their students to social dinners.
One of the hardest parts for me is the fast pace of change: the group of people I went out a year ago has hardly anybody in common with right now. It doesn't mean that there weren't some nice friendships, but it's so easy to lose contact. Still, I also feel that I made some friends-for-life as well. A lot of different ways also exist for meeting people outside of work, such as dancing, language classes, evenings organized in town for foreign "students"...