Now that SP1 is pretty much out there for Windows 7 and Windows 2008 R2 it’s far off time to start thinking about upgrading things in your Hyper-V environment.  I’ve been running the RC version of SP1 on my Hyper-V laptop for a while to get the benefits of Dynamic Memory and RemoteFX, but what about when I need to move over to the final bits?  Well this is the process taken from KB2489240 :

1. Start all of the virtual machines and upgrade them from the Beta or RC build to the released build of SP1 using the following steps:
  a.  Uninstall the Beta or RC build of SP1 on the virtual machine
  b.  Reboot the virtual machine
  c.  Install the released build on the virtual machine
  d.  Reboot the virtual machine
  e.  Shutdown the virtual machine
2. Remove the RemoteFX video adapter from each virtual machine using Hyper-V Manager or System Center Virtual Machine Manager 2008 R2 SP1

3. Upgrade the Hyper-v host from the Beta or RC build to the released build using the following steps:
  a. Uninstall the Beta or RC build of SP1 on the Hyper-V host
  b. Install the released build of SP1 on the Hyper-V host
  c. Reboot the Hyper-V host
4. Re-install the RemoteFX role service on the host(it will be removed in Step 3-a above)
5. Add the RemoteFX video adapter back to each virtual machine using Hyper-V Manager or System Center Virtual Machine Manager 2008 R2 SP1
7.  At this point the virtual machines should be able to boot up and RemoteFX sessions can be established to them

So why all this complexity?  Well you need to update the Hyper-V integration services and the operating systems on each virtual machine to get everything working just so.