None of the Meta questions I could find (I did a search and then trawled through the "bumping" tag) seemed to answer this.
What's the etiquette on answering a question with no posted answers that's really old and by a user that has left? If the question asker were still around, I think I could post an answer that would help them. But otherwise, I don't know if it's worth the bump to the question.
The question that prompted this was https://math.stackexchange.com/questions/40089/think-i-have-a-diffferent-idea-for-converting-angular-momentum-to-angular-veloci, but I imagine when trawling through old unanswered questions I'd find a lot of missing users.
In the particular case above, my gut says maybe flag it as too localized (although I've never done that and http://meta.math.stackexchange.com/questions/2698/what-does-too-localized-mean doesn't make me totally confident about when it applies), but I imagine some other old questions won't be close to too localized.