We are using EPDM 2012 and SolidWorks 2012 service pack 1. We did not use Solidworks 2011 or EPDM 2011, we went strait from 2010 SolidWorks and EPDM. The main thing that is different is the toolbox management from 2010, I guess 2011 started adding toolbox management as a option in EPDM. We had trouble with toolbox back in 2008 so we converted most of our toolbox parts to non-toolbox parts and managed them in EPDM. Many of our assemblies that had toolbox named parts tried to use toolbox parts from the C: drive so we had to re-point the assemblies to the toolbox named parts in the vault, once our assemblies were pointed to the vault toolbox named parts everything works good now. You may want to talk to your VAR about setting up your toolbox parts and the differnt options, they sent us a write-up on it.
I caught the blogs today from SWW on 2013. They said that backwards compatibility will be available in 2012 Sp5. That will be great when that happens. You want have to worry as much on when to upgrade!