Know why you're doing it.
As the article says, virtualisation is a strategic decision. The people responsible for company strategy and direction inhabit the boardroom (not the I.T. cupboard - if this is being driven by the IT dept, it's fundamentally running at the wrong level) and they should be able to complete the sentence:
"We are committing to Desktop Virtualisation in order to ....."
and that answers the "why are we doing this?" question. If you have the world's only talented IT director, that sentence will be followed by a qualifier "and we'll know it's succeeded when we can do <X> better/cheaper/faster/more reliably than we could before."