The new build has a build number of 12B17 and has "No Known Issues."
Apple has asked developers to focus on:
- Active Directory
- Microsoft Exchange in Mail
- PAC proxies in Safari
- Wi-Fi and audio when connected to Thunderbolt display
There are no release notes with any of the 10.8.1 builds. We most likely must wait for the official release to see what exact changes have occurred
If you are a developer, you can download this new build from the downloads section of the mac developer center.