May I say that tagging needs some attention at this stage. I think so mainly because for me, tags failed to help me find out whether a certain topic has already been discussed.
I see the following problems with the tags. There are many tags without a wiki now. Some tags are used for more than two topics (russian-usage) and there are two tags that at least partially refer to the same topic (vocabulary vs. word-choice). I've tried to write wikis for some of them, but it needs a systematic approach and somebody who can delete tags and re-tag, I guess. It would be a good idea to put the tags in order, don't you think?
And also, wouldn't it be a nice idea to write a FAQ about tags, how to use and create them?
Also I've got this idea that there should be tags covering all grammatical categories, like gender, number, case. Otherwise people will create more specific tags like future-tense or common-gender.
OK. I really want to systematize tags and hope that more people will join me here. So far, I've looked only at first 20 tags. I distributed them into following categories, marked the state of their wikis and written some suggestions about what questions they should cover. I'd suggest that if we agree on them, every person who wants to do it could take one or two related tags, correct their wikis and retag the questions. Or, if you feel like doing it, look at those tags that are not covered here and see if they need some attention.
usage (Done) The wiki is now OK. It covers questions on "how this expression \ word is used".
russian-usage (Done) The wiki is fine now. It covers questions on how Russian is used outside the Russian Federation.
word-choice (Done) The wiki is OK. Covers questions about difference between 2 or more words.
single-word-requests (Done) The wiki is OK. Should cover questions like "what word should I choose in this context?" No more mixed up with other tags.
vocabulary (Done) The wiki is OK. Let's have it as something that is opposed to the grammar tag and use for all possible vocabulary questions.
grammar (Done) The wiki is OK. Covers all possible things about grammar.
pronunciation (Done) The wiki is OK now.. It covers questions like "how is this word pronounced? what vowels are reduced in an unstressed syllable and how?".
spelling The wiki is OK. Covers questions like 187.
orthography The wiki is OK. Probably should be merged with "spelling". Let's keep both for the time being and see if they are really used for different things or not.
translation (Done) The wiki is OK. Covers questions like "what is the translation for?.."
english-to-russian Same as translation, is not used.
learning (Done) The wiki is OK. Covers requests for literature and resources on language learning.
etymology (Done) The wiki is OK. Covers questions like "where does this word \ phrase come from (as in question 366)". However, the question "why is it пить таблетки, not есть таблетки" should probably go to semantics, m?
Grammatical categories and parts of speech
adjectives (Done) The wiki is now OK, covers questions like 50 or 5.
nouns (Done) The wiki is now OK. Covers questions about grammatical categories of nouns, that is, when it is essential for the question that the words are nouns.
verbs (Done) The wiki is now OK. Covers questions about finite verbs as well as infinitives, participles, and gerunds.
plurals The wiki is OK. Covers questions about plural forms of nouns. Maybe it's good to add another tag for singulars or to rename the tag to "number"?
cases The wiki is OK. Covers questions like 404 and 168.
gender Wiki needs editing (although it's funny to have a tag for non-existent things like English grammatical gender). Should cover questions like 322.
All other stuff (a.k.a interesting phenomena)
mathematics (Done) The wiki is OK, thanks to KCd. Covers translations for mathematical terminology.
computer-science (Done) There's a wiki, covers computer science terminology.
loanwords (Done) The wiki is OK. Covers questions about loanwords.
expressions (Done) It has no wiki, covers multiword idiomatic expressions.