The values generated have some nice properties, but aren't random.

Converting the first 8 digits to an integer, hex2dec(left([guid],8)), the numbers have definate correlation with the previous generated value, and the 16th previous value, even when the generated ID are generated by deecidely unpredictable times (visitors to a website taking a particular action)

In the prize example, every 16th person might have a 10% or more greater chance than the others.