Quite possibly the single most inefficient spam filter to date. It succeeds in stopping very little actual spam, while blacklisting entire netblocks - and in the case of Brazil, entire countries. Their solution to finding a single spammer in a network is to list that entire network as spam-friendly, as well as any other ISPs who happen to be located in a 500 mile radius.
Getting removed from the blacklist is nearly impossible. There are obviously people in charge, as the list is always being updated, but you can never really contact said people if you're a legitimate business whose emails are being bounced by this glorious filter.
Why can't them crazy terrorists do something constructive, like taking out SPEWS?