updated 04:42 pm EDT, Wed July 10, 2013
No known issues
Apple is now seeding a fourth beta build of OS X 10.8.5 to developers. Listed as 12F20, the build follows one week after 12F17. There are no known issues, and Apple is again asking developers to focus testing on graphics, Wi-Fi, wake-from-sleep functions, mobile device management, and PDF viewing and accessibility.
Once it's finished, v10.8.5 may be the last major update for Mountain Lion. Apple is currently at work on OS X Mavericks, which will ship sometime in the fall. The upgrade will likely arrive simultaneously with new Macs.