I read this article on www.virtualization.info on how Microsoft and VMware use their own technologies internally. I find this an interesting idea, because it shows customers that you have confidence with your own toolset and can use it in a business-critical way. What is just as strong, if not stronger, is if partners and systems integrators (SIs) also are happy to use the tool internally. For SIs to do this shows then that they have the capability of rolling this out in a customer organisation themselves.
In enterprise sales, making the customer believe that the tool does what it says can be half the battle. Getting a good reference from a third party is always a valuable step, but developing a new product line and getting that first sale can be tricky without references. Becoming your own reference and showing belief in the product is one way of gaining that respect.
Secondly, to advise customers on important metrics and expectations based on your own experience at implementing the tool is a great way of spreading this message and gaining that belief. Microsoft's technet article advises on these experiences, showing that Microsoft gets 10.4 virtual systems on their 16 to 24 processor cores, and up to 64 gigabytes (GB) of random access memory (RAM) host machines.
Those interested can read in great detail about their configuration of these and other mission critical systems.
VMware published at their VMworld Europe 2009 conference their findings about using the ESX platform and that can be read about on http://www.virtualization.info/2009/04/how-microsoft-and-vmware-use.html. They also make use of their VDI desktop virtualisation as well.