The purpose of this thread is to propose candidate topics for writing canonical questions about (or using old questions for this purpose), and discussing them.
@JM suggested creating a set of canonical answers that we can mark recurring questions as duplicates of. Please read about the details here.
I think it's time we start collecting candidate posts to be repurposed as a canonical questions/answers.
If you notice a recurring question, please post a new answer where you list all related duplicate posts from the site (that are essentially about the same problem, even if they're not marked as duplicates). You can list posts from SO and MathGroup as well---these will serve as evidence that the problem/question really belongs in a FAQ. You can provide any additional relevant details or suggestions about what the canonical version of the question should look like.
Then the community can review these topics, select the truly FAQ-worthy ones, and move to the next step of writing up a canonical version of the question and answering it.