I actually just barely got out of a meeting about this. Hyper-V is showing signs of life. We just decided to build out a development Hyper-V instance. The primary reason for this is integration with TFS. Allowing our developers to create their own development environments is quite useful. VMware does have a product that competes against that, however it doesn't provide the integration with TFS that our developers are strongly pushing for.
For people that don't have developers on TFS that are pushing for this integration, I can see licensing being an important issue, as Jonathan mentioned. The fact that a fully licensed Hyper-V server can run unlimited Windows servers without additional licensing, that could have a large impact on costs. I don't imagine my company moving production servers away from VMware any time soon. However, between this POC for our developers and the licensing costs, the conversation will come up. We'll see if it ends up actually being a solid product we'd be willing to support.