VMware recently published, or updated, KB 1005760 which “will assist you with the troubleshooting of time synchronization issues within a virtual machine.”
I feel it’s noteworthy to point out that this particular KB article is for VMware ACE, Fusion, Server, and Workstation. It is NOT (repeat: NOT) for ESX and ESXi!
In fact, for ESX and ESXi the recommendations are directly the opposite. As per KB 1006427 (Linux) and KB 1318 (Windows) you should disable VMware Tools time synchronization and enable NTP or Windows Time Synchronization.
You may be asking why you’d want your VMs to do their own synchronization. There are a couple of big reasons. First, the VMware Tools time sync might run the clock backwards. One of the basic assumptions humans make, and build into things, is that time always runs forward. As such, things break when it doesn’t (apps, databases, filesystems, SSL, etc.). Second, it decouples your VMs from your infrastructure, so a vMotion from one physical host to another won’t change the VM’s clock. Doubly true if you have an ESX(i) host that isn’t keeping time right — that’s stays as an infrastructure problem, rather than becoming a service delivery problem (an SSL web server on a VM, for example).