UPDATE 03/30/2009: The slow network issues came back and progressively became so bad that I was experiencing permanent data loss due to connections timing out. I rebuilt the server last weekend w/o Hyper-V and everything is functioning normally. I came...
Man, this is one thing that had me going for a while. If you have instances setup to run under a specific user account (i.e. to auto-start on power up), you need to ensure that the user accounts have the proper permissions for all of the virtual files...