In listening to the pleading voices of many developers, the infamous Drupal 7 maintainer, webchick, just created the first unstable release of Drupal 7: Drupal 7 Unstable 1. Thank you, Angie!

These unstable release tags will probably never have actual release nodes, and they are before the beta, or even alpha releases, so you generally shouldn't use them on your production site. But, if you're up for an experiment in the bleeding of bleeding edge, try it out. I'm not too sure if they upgrade path will be supported, so we'll have to wait and see. I think I'll wait for the Alpha releases to update my site to Drupal 7 to be on the safe side.