In my experience it is dating between co-workers that is usually discouraged. I've never heard of regular socializing being frowned upon.

There is one slight exception. This is using work-time and the workplace itself to socialize. It is something that ought to be left for outside of the workplace. It cuts down on efficiency but, more unfortunately, it really makes someone whom is left out socially feel terrible. I have had to council subordinates on this; that, if they can't include person X in their workplace socializing then they shouldn't be doing it at all. It is simple etiquette I've had to remind people of - frequently. This especially goes for talk in the workplace about planning out activities or reminiscing about those that have already occurred in front of those that are unwelcome to participate. Kind of a no brainer. I did not ask that people not be friends rather that their friendships wait until after the business day is complete.