Here’s yet another new feature for 2013. When you create an opposite-hand version while mirroring a subassembly, all the standard mates in the subassembly are mirrored as well. Previously, standard mates within the subassembly that mated to the default planes or origin of the subassembly were not created..
A quick video on the new feature
Need more on what’s new in SolidWorks 2013, visit new SolidWorks 2013 website to see all the major updates when it launches on September 10, 2012.