Something I had always looked for, for my own information and from a marketing perspective was a solid performance comparison between what could be considered the big 3 hypervisors.
There are a number of these “lab tests” out there (and most look to be dated) but this is current and covers most of the points I was interesting in reading about.
I recommend having a look at the following post and I also recommend looking around the rest of the site. virtualizationreview.com has a ton of virtualisation related information and is usually presented in a complete and unbias fashion.
http://virtualizationreview.com/articles/2009/03/02/lab-experiment-hypervisors.aspx
Blog, Citrix, Virtualization, Windows
virtualization, esx, xenserver, hyper-v