As far as I can tell, most functionality is in and this beta is very close to the public release. The UI seamlessly blends elements of OS X Lion and iOS, using iOS-style alert pop-ups, but the look of Lion iCal for example. See the video for a sneak peek. Thanks to YouTube user helpfulmactips2010 for posting.
While it first appeared that Apple accidentally leaked the beta to non-developers, this was quickly corrected.
iCloud is Apple’s cloud storage syncing solution for iOS devices which was announced this past June. The general release is expected this spring.