CNET Asia published a long comparison between Virtual Server 2005 Release Candidate and GSX Server 3.1 made by RMIT IT Test Labs.
I personally don’t like it very much because reviewers approached both products like a simple desktop application (you can notice this starting from testing platform: much more a desktop machine than a real middle business server) and left out a deep analysis of how virtual machines processes are handled (which impacts on VMs performances, stability and management).
It’s also incomplete becase Virtual Server 2005 pricing was not published at writing time.
Anyway it’s a good starting point to have an idea of raw features available.
Read it here.