In short, it looks like Microsoft has right-sized its licensing with what people are doing already. From Keith Ward over at Redmond News:

Microsoft has made substantial changes to its virtualization licensing program, changes that will lower the cost of using virtualization for many customers.

In a document released yesterday, Microsoft relented on a key issue that should ease the financial burden of virtualization: the 90-day license transfer restriction. Under that rule, a program, such as Exchange Server, could be moved from one physical server to another, but could not be moved again for 90 days without paying an additional license fee for the new host server.

In effect, it meant that companies with two or more servers could not move Microsoft products to different servers without buying a license for each server. With virtualization, programs are moved around frequently, so the 90-day restriction was a stumbling block to adoption of Microsoft virtualization technologies.

I would argue that many environments have been unknowingly doing this anyway. So, this change only aligns "what is legal" with "what is being done".

For more, including a link to the actual licensing verbage, check out: http://redmondmag.com/news/article.asp?editorialsid=10135