System Center Virtual Machine Manager 2008 has been announced at MMS:
Also announced was this (I believe) previously undisclosed feature:
System Center Virtual Machine Manager 2008 tightly integrates with Operations Manager 2007 to deliver a new feature called Performance and Resource Optimization (PRO). Using deep knowledge of the IT environment including operating systems, applications and hardware, Operations Manager identifies opportunities for more efficient physical and virtual resource allocation and generates “PRO tips” within the Virtual Machine Manager console. Administrators can implement these PRO tips and dynamically optimize their datacenter based upon pre-defined policies and the real-time, changing demands of users. When used in conjunction with the broad System Center management suite, System Center Virtual Machine Manager 2008 enables customers effectively to manage both their virtualized and physical servers and applications across their desktops and datacenters with a single set of consistent, compatible tools.
More announcements and links can be found at the System Center home page (the link to the beta doesn't seem to be working yet)
and more details
Keith has a TOP 10 features list on his blog
Microsoft Virtualization Team blog - more features are listed including a screen shot or two and VMware management comparison.