Note that it's also good to have some preliminary discussion here, moving on to e-mail mainly if personal details come up that one feels unwilling to share in public. If a lot of people publicly post their interest to participate, then that will encourage others to apply as well. Plus it gives people a picture of what sort of other folks they might end up working with. Also, discussing the details of the issue in public will help those who might initially be too shy to send a private e-mail, as they can just read what's been discussed before. Even if you weren't shy as such, others might raise questions you didn't happen to think of. For instance, I think Anna's four points above are good advice for a lot of people, and I'm happy that Yorick posted the comment that prompted this response and didn't just e-mail Anna directly.

(EDIT: Removed a few paragraphs as I realized I'd have to rethink their content.)