Microsoft has a TechNet Wiki that lists all of the relevant updates and hotfixes for the Hyper-V Role or Hyper-V Server 2008 RTM/R2.
The last update to the Wiki was October 26, 2011.
Also, the Wiki has an RSS feed:
A snip of the Wiki page:
The second from the bottom update dated October 20th looks to be one of the latest on this list as of this writing.
For those of us running virtualization solutions on Hyper-V and failover clusters on Hyper-V this list is very important to monitor.
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book