I think these videos are really great. There is so much confusion about MEF and here you dive into details of what it can really do from practical point of view. This is really in your stile of explaining practical side of technology. However your videos still leave me wonder what MEF really is for .NET from architectural point of view. MEF codeplex site attempts explaining it, but it doesn't seem clear to me. It seems like MEF is really abstract componentisation approach of whole .NET (with one default implementation). However this implementation seems to be replacing such existing frameworks as Unity. May be new video on architecture?