Thanks to VMGuy.com for the detailed info below.

The maximum uptime solution for vCenter has been upgraded to 5.5 Update 2 and can be downloaded here.  Here’s the what’s new section from the release notes:

Support for Windows Server 2008 SP1 and SP2 (x86/x64) — VMware vCenter Server Heartbeat now supports running on Windows Server 2008 SP1 and SP2 (including x86 and x64 versions) operating systems.
Support for Windows Server 2003 Enterprise SP2 (x64) — VMware vCenter Server Heartbeat now supports running on the Windows Server 2003 Enterprise SP2 (x64) operating system.
Protection of VMware vCenter Management Web Services — This release of VMware vCenter Server Heartbeat adds the vCenter Management Web Server to its list of protected vCenter Server components.
Introduction of the WinZip Self-Extracting executable file for Setup — Installation and setup of VMware vCenter Server Heartbeat is initiated through the use of a WinZip Self-Extracting executable file.
60-day evaluation mode — This release of VMware vCenter Server Heartbeat provides a built-in 60-day evaluation mode that is triggered from the date of installation. Either prior to or upon expiration of the 60-day evaluation period, administrators will need to provide a valid license key to continue to leverage VMware vCenter Server Heartbeat functionality.
Tomcat Monitoring Rule — A new rule has been added for vCenter 4.0 Tomcat Web Server availability.
Note: The term vSphere Client is applicable to both vSphere Client and VI Client except where VI Client is specifically stated.