The latest Lion Developer Preview (released yesterday) features some cool new redesigns of a few of Mac OS X's built-in apps. First up is a completely redesigned iCal. The new iCal now closely resembles the Calendar app that you find on the iPad. It sports a leather header, complete with strips of torn away calendars. The overall look and feel of the new iCal, like its iPad counterpart, now closely resembles a physical desktop calender.
Another redesign, though less noticeable than the new iCal UI, is an updated iChat UI that combines AIM, Jabber and Bonjour contacts together in one window. This is a welcome tweak, as iChat previously separated all your different contacts into separate windows.
With the above changes, and the fact that Address Book in OS X Lion already got a similar overhaul so that it closely matches the Address Book app on the iPad, I wouldn't think it's too much to hope that Game Center for the Mac App Store and iBooks for OS X is too far off.