Apple has seeded build number 12b17 to developers and AppleSeed members, after last week’s initial release. The build has no known issues, which could mean that the release is coming sooner rather than later, but Apple is asking developers to focus on Active Directory, iCal, Microsoft Exchange in Mail, PAC proxies in Safari, SMB, USB, along with WiFi and audio playback when a machine is connected to a Thunderbolt external display.
While it was previously believed that 10.8.1 would see a public release around the rumored September 12th event, it now seems that Apple is pushing for a more agressive release. Updates immediately following a large 10.x upgrade generally focus on stability and performance issues that could have arisen on particular machines during the upgrade. Mountain Lion has, however, been one of the smoothest upgrades in years, with little to no issues being considered widespread.