Consider this question: Can't get results from a JSON API.
It has just had a new tag, untappd, applied to it, and the author that has created the tag has also now suggested contents for a tag wiki for it (see https://stackoverflow.com/suggested-edits/243656 at present). There is only one question tagged as such and no other questions about it in the system.
I would consider this "untappd" social network to be an obscure resource and not likely to be used again ("too localized" as a tag). Wikipedia has rules requiring certain degree of notability before an article may stand; does Stack Overflow have such rules or guidelines? Should such a tag be permitted to remain? My inclination would be no, but I didn't want to just untag it without some discussion first.
One aspect of this question can be extended to cover Stack Overflow specifically; there might be a difference in notability guidelines on different categories; for example, languages, libraries, websites (untappd fitting into the last category). At this level, I suppose it might be becoming a question of suitability almost as much as notability. I feel that a website requires a lot more notability before it's suitable than a language or library would.