New performance results are out that show ESX supports more XenApp users with lower CPU usage than XenServer. Click through for the whole thing, including the details of the user-centric workload. For perormance testing of desktop or terminal services virtualization, simulating the workload is very important. It can be tricky, and if you don't simulate how real humans use their desktops, you may not come to conclusions that can apply to real-world deployments.

VMware: VROOM!: Virtualizing XenApp on XenServer 5.0 and ESX 3.5.

has always been interest in running Citrix XenApp (formerly Citrix
Presentation Server) workloads on the VMware Virtual Infrastructure
platform. With the advent of multi-core systems, purchasing decisions
are driven towards systems with 4-16 cores. However, using this
hardware effectively is difficult due to limited scaling of the XenApp
application environment. In addition to the usual benefits of
virtualization, these scaling issues make running XenApp environments
on ESX even more compelling.

recently ran some performance tests to understand what can be expected
in terms of performance for a virtualized XenApp workload. The results
show that ESX runs common desktop applications on XenApp with
reasonable overhead compared to a native installation, and with
significantly better performance than XenServer. 

and other products that virtualize applications are prime candidates to
be run in a VM. These results show that ESX can do so efficiently
compared to using a physical machine. This was shown with a benchmark
that: represents a real desktop workload, uses a metric that includes
latencies of all operations, and requires that all operations complete
successfully. Furthermore, ESX supports about 13% more users than
XenServer at a given latency while using less CPU.