Just a heads up. According to the Release Notes PowerCLI does is not supported

Does this mean that it will not work – No of course not!  From what I have tested it works almost flawlessly – but there are some quirks…

For example - Set-NetworkAdapter returning 'Operation is not valid due to the current state of the object' and Error with Move-VM: Operation is not valid due to the current state of the object.

And as Luc put it, “Well, you can't file a bug for something that is not supported, now can you “

Update – February 12th, 2013

VMware have now released an updated version – see the announcement here - PowerCLI 5.1 Release 2 Now Available

This will actually render this blog post obsolete – but I am happy VMware have addressed this issue.