Even as OS X 10.8.1 was made available to the public, Apple has seeded the first beta of OS X 10.8.2 to AppleSeed members and developers. While 10.8.1 now seems more of an update to fix bugs and battery life issues, 10.8.2 looks to be the release that will include more features.
Most notable is the integration with Facebook. While Facebook integration has been available as a downloadable add-on for developers who are testing Mountain Lion beta builds since the first developer preview, it has always been buggy and had issues (such as contacts being overwritten). Apple seems to be giving it more attention now that Mountain Lion has been pushed, and the various issues are beginning to clear up.
Also included is the merging of iMessage phone numbers with email accounts. With this included, the Mac’s Messaging app will be up to par feature wise with the iOS version, and be able to incorporate both emails and actual numbers for sending and receiving messages.
The build is available via Apple’s Developer Connect.