vSphere 4.1 update 1 available
If you miss it: VMware vSphere 4.1 Update 1 is generally available as of February 10, 2011.
You can find the releases notes here:
From my point of view, the most interesting features are the support to 160 logical processor and the support to RHEL6 and RHEL5.6 (and their customization) as guest. Also there are a lot of bugfixes: in my environment the most critical are about bnx2 nic.