An opportunity to share one of my favourite StackOverflow questions of all time!

It's well worth reading through the answers and the comments, but here's a little sampler platter:

This will run for a lot more than hours. Assuming it loops at 1 GHz (which it won't - it will be a lot slower than that), it will run for 10790283070806014188970 years. Which is about 83 billion times longer than the age of the universe.

damn - so maybe serveral threads generating guids is a better idea?

4 threads on a quad core processor would make it run in 20 billion times the age of the universe - so yeah, that would help a lot.