A few weeks ago I updated our vCenter instances to 5.5 Update 1a to address the Heartbleed vulnerability. Now Update 1b has been released with further OpenSSL updates, plus host profile and VSAN fixes (blog).
Normally, my update procedure involves extracting the downloaded ISO and installing after that. Today, I decided to simply mount the ISO in the vCenter server running on Windows 2012. That led to my only issue in the upgrade procedure, a problem noted in VMware KB 2050539 but which appears to apply to more than just “VMware vCenter Server 5.1.x”.