I think that by now the WordPress post formats aren't extensible by the users, so I suggest another one for consideration in the future. May be called "question" and is based on an answer of a given question. It is used by formspring.me and also used as an own post type by Tumblr, although not from the front end because they are created by answering actual internal messages sent though the site. Here's a possible implementation:
- A form on a WordPress page is used to submit the questions. The fields are much like the ones for comments: name, e-mail, URL and question. If one is logged on the site the first fields are auto-filled. This generally is deemed as plugin territory, but considering that the last version is adding some admin functions to the front-end, it should be something possible to do with the API. Not sure how to filter spam, though.
- Then, in the admin post view, all "questions" submitted appears as draft posts, with the "question" post format, with the question itself as the title and the name, e-mail, and url fields at some custom metabox
- One uses the "body" metabox to answer.
This is kind of the ideal thing, but one may be able to use the "question" post format on the fly even if the question was not sent by anyone by any other form.