>For example, if the workstations should periodically synchronize their clock >with the server, or some external reference (sometimes necessary) then their >clock can go backwards then the possibility of creating a duplicate key is not >zero and will be proportional to the adjusted time (for example if the adjust >was only .1 second the collision will be less probable than a 10 minute >adjustment).

I over-simplified in my explanation. CoCreateGuid uses the following to create the GUID:

1. NIC address. This assures that the GUID is globally unique.
2. System clock time. This assures that the GUID is unique to the local machine, as well as globally unique given #1.
3. A pair of persistent counters that will account for system clock scenarios as you mention above. This assures that the GUID is unique, even if you reset the system clock, or if the OS resets it for Daylight Savings Time (for instance).