A just appeared post on VirtualCenter newsgroup reports that GSX Server 3.1.0, expected for this week, is delayed cause a memory leak found in code.
This post also leak the information about a new VirtualCenter update, 1.1.0, expected to release at the same time. As consequence of GSX bug, VirtualCenter 1.1.0 is delayed too.
The new release date for both products seems to be the 9th July.