The Facebook Aperture Plugin is a project I plan on tackling over spring break (next week). On March 15, Facebook released an export plugin for iPhoto that uploads your photos to your Facebook account; they have also the released the source. Aperture has a publicly-available plugin SDK, which should make putting together such a plugin relatively easy. I'm also guessing that a lot of the code from the iPhoto plugin can be reused.
Stay tuned.