If you doing doing web related work on the VMs and getting an Unauthorized response have a look at this note http://blogs.msdn.com/lcash/pages/network-authentication-issues-on-vpc-refresh-1.aspx
Which is related to this Microsoft KB article http://support.microsoft.com/kb/896861
So if you get this error “HTTP 401.1 – Unauthorized: Logon Failed” on the VM when doing anything related to the web page like developing on EP development then it is usually a result of this loopback issue because of the use of host headers in IIS.
As a side note to this. If you build out a Windows 2008 machine and are using host headers like we do on the demo VM then you will need to do both methods as described in the KB article. That is create the DisableLoopbackCheck registry entry and also specify the BackConnectionHostNames registry entry.