Apple has just rolled out the latest update to Mountain Lion with fixes to a number of issues users have been experiencing lately. If you haven't already noticed the prompt, you'll find OS X version 10.8.5 is now available in your Software Update queue or directly from here.
The latest update is said to improve upon and fix a number of issues including file transfer performance over 802.11ac Wi-Fi. Some reports claim the 802.11ac file transfer speeds are more than doubled compared to in 10.8.4. Additionally, the update tackles recent problems with displaying messages in Mail and resolves an issue that was preventing screen savers from starting automatically on some machines.
Other updates with 10.8.5 include improved Xsan reliability, more stability with large file transfers over Ethernet, improved Open Directory server authentication, fixes with smart card integration in System Preferences and some of the additions that came along with the MacBook Air (Mid 2013) Software Update 1.0.