It really depends on the culture of the work place and the individual people. I have coworker or colleagues who I am also friends with. We hang out outside of work and don't talk about work at all. I have one colleague who likes the same tv show as me, and we text each other while we watch it on Friday nights. I think it's few and far between co-workers you will actually develop a close relationship with, as in a friendship and not just an aquaintanceship. I regularly try to have drinks or socialize with coworkers at happy hour or whathaveyou, just to encourage the team mentality and let them see me as a person (I'm upper management). I've also found getting to know a bit about my coworkers personally helps me in relating to them in the work place. When I know what's important to them, I know how to appeal to them to get the best performance out of them.

However, I also hate mandatory work socialization events. One of my previous employers expected us to spend all our free time and holidays and weekends "being friendly" with them and the rest of the staff, and it felt like I spent 24/7 working because they'd also invite patrons and donors. So it wasn't even like you were just chilling with co-workers.

The thing is, it's really great when you make a friend at work, a real friend, but I would say it's uncommon, because we're not there to make friends. We all happen to work at the same place, that's all. It doesn't mean you hold the same values or have the same outside interests or anything in common beyond being employed by the same company. And work friends often fall off when you don't work together anymore.

Seesaw