Latest update to OS X Mountain Lion (10.8.4)
... should be out sometime next week.
I have it on good authority that the testing is complete ... should definitely be released PRIOR to the start of WWDC on June 6, where no doubt, OS X 10.9 will be revealed and discussed.
For me, the biggest fix in 10.8.4 is that the nasty REPLY-ALL bug is fixed... plus:
• Compatibility improvements when connecting to certain enterprise Wi-Fi networks
• Microsoft Exchange compatibility improvements in Calendar
• A fix for an issue that prevented FaceTime calls to non-U.S. phone numbers
• A fix for an issue that may prevent scheduled sleep after using Boot Camp
• Improved VoiceOver compatibility with text in PDF documents
• Includes Safari 6.0.5