When powering on a virtual machine, have you ever come across this error message? The parent virtual disk has been modified since the child was created. Or perhaps you are unable to remove snapshots for virtual machines on one or more datastores. That one I know causes many calls into Support.
There are several cases where you may encounter Snapshot issues after experiencing issues with a virtual machine. We've just updated KB 1007849 to include a video:
The KB and video applies to ESX 4.1 and earlier. This is not for desktop virtualization products.
Note: If you want to commit a snapshot using the command line, and you are not experiencing these issues, you can use http://kb.vmware.com/kb/1006847. This article has a video that can help walk you through the process.