It contains support for 4K@60Hz on late 2013 rMBPs and the new Mac Pros. It also includes a Safari update and other minor improvements. If you have a newer Mac and a 4K monitor.....time to purchase a Panasonic GH4 and shoot some 4K videos!!!
I am waiting for the Apple monitor range update so I can justify changing my current 30" external screen OSX Update went fine....
One week from tomorrow we have WWDC. With luck all kinds of goodies will appear such as Thunderbolt Display 2, Aperture X, and faster/cheaper MacBooks.
