Does this foreshadow any changes in iLife or iWork? Does it break anything in iWeb?
Mountain Lion now has access to iCloud's Documents in the Cloud, and Apple showed us a version of Pages that worked with that feature. That's a stealth announcement of a new version of the iWork Mac apps that will support Documents in the Cloud on Mountain Lion. It would be nice to see such an update of the iLife apps too, allowing users to transfer projects to and from their devices without wires or iTunes File Sharing.
iWeb is still functional in Mountain Lion, but seeing as how MobileMe hosting for websites is being discontinued this June and Apple shows no interest in updating the app, it might be time to look at alternatives.
What's this I hear about the Mac App Store and Software Update being merged?
You heard correctly. The Mac App Store will now be the sole place for Apple software updates. When new software is available, you'll receive a notification in Notification Center; you can download it by opening the App Store app and selecting the Updates tab. Notifications also carry over to any Mac App Store apps, as well, meaning that you no longer need to perennially leave the App Store open to check for new updates to your programs.
What's new with iCal and Address Book, besides their name changes?
We've spent a little time with both Contacts and Calendar; both sport interface changes, including a three column view in Contacts and a left sidebar for calendars in Calendar. Apple's scheduling app also sees the removal of to-dos (which head to the Reminders app) and integration with the same advanced search tokens used in Lion's Finder and Mail.
Does Dashboard get any love? How about Launchpad?
Surprisingly, yes. Dashboard receives a new widget browser reminiscent of Launchpad (or the iOS home screen), along with a search bar along the top; it's to be determined whether this means Apple may be interested in porting over more iOS-like widgets, but color us intrigued.
Launchpad gets a small tweak--a search bar, present at the top of each Launchpad screen.
What does Game Center on the Mac mean for games on the Mac?
We'll have to wait and see until Mountain Lion actually comes out, as Game Center isn't very useful without apps that utilize it. That said, your iOS Game Center accounts will carry over, and you should be able to do many of the same things you use Game Center on iOS to do--invite others to games, keep track of achievements, and find new things to play.