In my opinion noun tags should be in singular form unless there is a really good reason to use the plural form. I would much prefer "buffer" over "buffers", "file" over "files" etc. Usually when a question applies to foobars it also applies to a single foobar.

Of course there are always exceptions to a rule: for instance, when tagging questions related to multiple modes then the plural form "multiple-modes" comes naturally and should be preferred.

Should we use "buffer" or "buffers", "file" or "files", ...?

EDIT: I realized that I included my opinion into the "question", sorry for that. I will instead answer my own question with my opinion.