In visual studio 2012 if you launch it as administrator and go to file open, it will not see any drives that you mapped using the subst command.
for example, for flexibility over vpn we utilize a method in order to reference our assemblies locally, so we may map a link to a local folder on our hard drive which are a copy of the production assemblies. subst x: c:\tempassemblies. It works fine in visual studio 2008 and visual studio 2010, but does not work in visual studio 2012. I tried running it as administrator, i really can't think of anything else i can do in order to make this work.