We have been slowly moving users to the new GNOME desktop and the results have been excellent. The server is a 4 processor, quad core HP and today we hit 75 concurrent users. CPU usage is under 1% and memory consumption is not bad at all. Unless we hit some as of yet unknown limitation, it looks like we could get a full load of 300 concurrent users pretty easily.
It's interesting that the highest amount of CPU is being chewed up the Citrix client (wfica) which seems to be very "talky". We are in the process of moving to 100% RDP as our connection technique to Windows, so in the coming months those will all go away.
Very promising start to the migration process.