There is a discussion about drupal.org soon promoting drupal answers and the number of questions could explode.
I think it would be really useful if we could filter questions by modules referenced in the question. For example, I might want see all questions related to the flag module. I could envision a "Questions & Answers" link on the d.o. flag module page that will then show all related questions on d.o.
Rather than using more tags (don't think we want 10,000+ tags added), how about creating a search based on the links in the question? Most questions already have links to module pages.
The same might apply to the API pages ...