I just saw a proposed tag for "Facebook" based on (I believe) one question; further, I voted to close that question.
Do we need a tag for "Facebook"? Does having extra tags in the system do any harm?
I believe that for the time being there is no reason to add a
If questions about social network statistics start gaining momentum we can start differentiating then. As it stands, having a single question using a tag is pointless.
Not much use in closing the question now; at present, it's 11th most popular, and poised to continue climbing. I shared that initial impulse though, FWIW. I find its popularity useful for redefining the utility of CV as a whole—not that it needed redefining necessarily, but I think I understand it better now, thanks to this question.
As for facebook, one question certainly doesn't make the tag needed. Searching for "facebook" yields 66 hits at present though, so if facebook is going to be useful, it should probably be applied to some of those other questions (of which there are less than 66, because that number includes answers). That being said, those questions may not be about Facebook, so if too few of the questions actually are, the tag seems quite useless from an empirical perspective, for now.
Furthermore, since social-network already exists, has been used 21 times, and has a good, non-redundant wiki and excerpt (facebook's are redundant), the synonym suggestion,
"facebook$\rightarrow$social-network" would naturally find its way to a meta-question like Current tag synonym candidates, by my own hand if no one else's.
Since the preceding answers argue for this synonymity as well, and have received their share of upvotes already, I've submitted an edit to the question in question that replaces facebook with social-network (among some other pretty trivial changes). It got accepted, so I guess that's that? facebook now appears on zero questions! I suggest it be removed entirely...though this will happen automatically if it remains an orphan for six months.
social-network might fit on some of those questions that mention "facebook" though, so there may remain some work to do, depending on whether editing those questions is worth bumping them up in the active questions list. This (and the OP itself) raise a number of related meta-questions: