There have been some changes to its calendar, iCal, including adding simulated leather stitching, but also "iChat’s main window houses AIM, Bonjour and Jabber contacts together like Adium," writes 9-to-5 Mac.
I don't know of anyone who really cares that much about calendars, electronic or not, but the new iChat bundling contacts together in buddy lists could be convenient for users. But isn't that damning Lion with faint praise? One of the new things about Lion was going to be how it better handled internal errors and software crashes, but at least one reviewer said that his Chrome browser was constantly crashing.
I agree that it's unlikely this second preview is the last. My money's on Apple unveiling the new OS X Lion at its Worldwide Developers Conference in June, especially since it's putting so much emphasis on Mac applications.