Once in a while there's an incremental OS X update with a ton of bug fixes. This is one of them. Check out the list for 10.8.4:
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
Improves VoiceOver compatibility with text in PDF documents
Includes Safari 6.0.5, which improves stability for some websites with chat features and games
A fix for an issue that may cause iMessages to display out of order in Messages
