Mountain Lion is here!
Coming this month: Mountain Lion introduces more than 200 innovative features including the all-new Messages app, Notification Center, system-wide Sharing, Facebook integration (will come later), Dictation, Power Nap, AirPlay Mirroring, Game Center, and the enhanced security of Gatekeeper. iCloud is also built in to the foundation of OS X.
Mountain Lion is now available as an upgrade from Lion and Snow Leopard, from the Mac App Store, for $19.99.