Yesterday we pushed the first release candidate for bbPress 1.0 out the door. You can grab it from the download page.
Over the next few weeks there will be a (relatively) rapid progression of “RC” releases as we move towards a final release of 1.0
bbPress is almost stable enough to use on a live website, but I can’t recommend that yet. If you want to try it out on your existing data, then I suggest you make a complete copy of your site and then upgrade. If you just want to take a look and see what’s changed then try a fresh install (some independent testing of the installer is always useful).
If you find a problem please report it in Trac so I can get onto it as soon as possible.