a small update via Software Update, and then you can download Preview 2 from the Mac App Store.
There has been some speculation that Apple is getting close to a release or Golden Master build, but judging by 9to5 Mac's initial findings there's definitely some way to go. The Golden Master will probably appear at, or just before, the Apple WWDC in June.
So far, it's looking like the only changes in Preview 2 are the leather bound iCal skin that you can see above, and the main iChat window now combines your AIM, Bonjour and Jabber contacts, like Adium. We're sure that more details will emerge throughout the day, though, and there's bound to be lots of invisible changes, too. We'll update this post when we find out more.