VMware released vCenter 2.5 Update 5. The release notes state:

VirtualCenter 2.5 Update 5 includes significant performance and scalability improvements to VMware HA. Use VirtualCenter 2.5 Update 5 for environments with more than 35 virtual machines per host in an HA cluster.
For information on the ESX Server host settings required for this scalability improvement, see ESX Server host settings required for environments with up to 80 virtual machines per host in an HA Cluster (KB 1012002).

KB 1012002 states that with vCenter 2.5 update 5 an ESX host in an HA cluster can support up to 80 VM’s. The article continues with the specific ESX settings that are needed. The “RunningVCpuLimit” needs to be set to 192, the Service Console memory needs to be raised to 512MB and the Host Agent (hostd) memory settings in /etc/vmware/hostd/config.xml need to be increased. Note that the ESX host will need to be restarted after changing the Service Consle memory allocation.

In addition to the HA change, the release adds new http connection timeout settings:

A new advanced setting entry vpxd.httpClientIdleTimeout can be used to configure the timeout value for an idle HTTP connection. The default value for this entry is 15 minutes (900 seconds), ensuring that the VirtualCenter Server closes the idle HTTP connection after the connection has been idle for 15 minutes. If a firewall session timeout value is set to less than 15 minutes, the value for vpxd.httpClientIdleTimeout should be changed to be smaller than the firewall’s timeout value.

No updates to the vCenter Enterprise Converter or Update Manager plug-ins have been made.