When VMware issued VirtualCenter 2.5 Update 1 and ESX 3.5 Update 1 in April of this year, I felt that this release was mature enough to upgrade my environment. One observation I have made is related to the VMware Infrastructure Client (VIC) versioning. The VMware Infrastructure 3 release notes mention many configurations related to supported environments of VirtualCenter and ESX, but do not distinguish between the base release of the VIC for VirtualCenter 2.5 and 2.5 Update 1.
The VIC for VirtualCenter 2.5 (base release) has a build number of 64192 whereas the VIC for VirtualCenter 2.5 update 1 has a build number of 84767. Unlike the upgrade from VirtualCenter 2.0 to VirtualCenter 2.5, connections into VirtualCenter are not prompted to download and install the new version of the VIC. Therefore, you can have VIC installations with the older version interacting with the newer VirtualCenter server. I recommend that you enforce the version currency of the VIC on all systems connecting to a VirtualCenter 2.5 Update 1 to be at build 84767 so that commands match the capabilities of VirtualCenter. For most situations, this is not going to be an issue, but should you use VirtualCenter plug-ins, advanced features, or have a large amount of VIC traffic there may be some anomalies in the version mismatch.
The figure below shows two information screens from two installations of the VIC. Both of these installations are interfacing to the same VirtualCenter server, but the top one is at the current version:
During the VirtualCenter upgrade process, the VIC is updated locally on the server. Further, unlike the VIC for VirtualCenter 2.0 the VIC for VirtualCenter 2.5 and 2.5 Update 1 have the same binary update path, so you will not have to manage two shortcuts for access.