I heard it's like a lottery ban. All the registration numbers are spun in a big ball and one or two are drawn whenever Jim feels like it.
It gives new meaning to the phrase, "Your number's up."
I heard it was all driven by really cool Perl scripts... it generates a random string, then does a String Compare, finding the n closest matches (where n is a number the user configures to their personal preferences). Then, it randomly generates a number based on n, and it then bans that user...
I heard it was paid for by a grant from the RNC...