The full release isn't due for some time and will probably coincide with the release of the Boxee Box. Still, the beta is exciting -- until recently, only alpha releases have been available. Many new features appear in the beta, such as searching and additional content partners.
The beta is only "officially" available through Boxee, and won't be ready until January. Whether they will try and stop this unsanctioned version from being distributed remains to be seen -- it is freeware, after all.