From the horses mouth: Official release notes regarding VMWare ESX 3.0.1 and VirtualCenter 2.0.1 changes.

I am particularly interested about the following:

VMware HA May Incorrectly Handle Temporary Host Network Isolation

In VMware HA, host network isolation detection occurs within 15 seconds of host isolation. After a failure is detected, all virtual machines are failed over to other hosts. If the network connection is restored before 12 seconds have elapsed, other hosts in the cluster do not treat this as a host failure, and the virtual machines remain powered on on the original host. After 12 seconds, the clustering service on the isolated host shuts down and the virtual machines are powered off. If the network connection is restored shortly after 12 seconds, the virtual machines are not started on other hosts because the host is not considered to be isolated. As a result, if the network connection is restored shortly after 12 seconds after the host has lost connectivity, the virtual machines are powered off but not failed over.

I have not had this issue, but it certainly would give me a scare if it did happen.