I concurr on the MEF with PRISM v2.  There is MEFContrib that has a MEFBootstrapper but it does not work with the latest release of PRISM and MEF in VS2010.  It seemed like they were on the right track, but got diverted.  I want to pick and chose when I use PRISM and MEF.  My two cents is that PRISM is to complex for an average developer, MEF is easier to use and has more utility around creating and traversing through catalogs.  I just can't inject into a Region without PRISM.