Which is easier? Bringing someone up to speed on the .NET platform or bringing someone up to speed on your business? This is the question that project managers should be asking themselves when converting an old project such as MFC or C++/COM to .NET.
This is not the first release for .NET. Indeed it has been released for five years already (not even counting the large Beta period). The number of assemblies and types to learn is enormous. That is a lot of knowledge to absorb. In fact the longer companies wait to go to .NET, the more learning they have to do.
The productivity gains from .NET are significant, but think of all that time spent just getting back to the level of competency where you are right now. When starting on a major refactoring of the current product, it makes more sense to keep only those developers who have a ton of accumulated business knowledge. Then hire a bunch of expert .NET developers and do a lot of paired programming to get the knowledge to transfer between the groups.