When inserting a part into an assembly if you dropped it onto the origin of the assembly that part would be fixed in place with all of it's planes matching the master assembly. This used to work with sub-assemblies as well. It does not work for me in SW2012 in either the x32 or x64 version. I try to drag them in and fix them on the origin and they end up in a random location instead. This means that I need to mate them in place manually. Of course there are many sub-assemblies that I need to do this with anyways, but it is inconvenient that this does not work anymore for times when it would be nice to do.