Yesterday Apple published an Update to the Developer Preview of Mountain Lion. Its available in the App-Store which completely replaced the regular Software Update.
At first glance the notification center got updated with the possibility to easily disable any notifications, an feature that surely will be introduced in iOS 6 as well.
The system seems overall a lot more responsive and faster then the previous developer builds and it also seems to fix a few issues i had with DP3 like a freezing Dock.
Another feature we gonna see in iOS 6 is the user verification when Applications try to access your contacts, this was introduced in an earlier build but its actually the first time i saw the dialoge.
Read more about Mountain Lion.