If you’re a XenApp user making a virtualization platform choice you need to read the new Project VRC paper that came out last week NOW. The paper is titled, "VRC, VSI and Clocks Reviewed". The results have shifted dramatically since the January findings. Instead of trailing, ESX 4.0 now has a 4% advantage over XenServer 5.5 in the number of Terminal Services users it can support on a server.
You can read the VRC whitepaper here (requires free registration).