[eluser]slowgary[/eluser]
No it isn't. UUID generation is partially based on time, so a UUID you made 20 minutes ago will never have been made again whether you made it or not, right?
Also, I'm sure a UUID that you create could be duplicated in the world somewhere. It's not as if UUIDs are registered in some centralized system where they're only allow to be used once. Part of the probability of duplication is likely based on the fact that not every piece of software in the world is working off of one database, otherwise UUIDs would certainly be duplicated.
If I must, I will engineer a million unit bot-net to generate constant UUIDs and register them in a data center the size of Google's, just to calculate the frequency of duplication, thus proving you and many others from the cult of UUID wrong. ;-P