The Policy Block List is a great idea, the ISPs can state which of their IP blocks should be sending mail through their relays, and not direct to your servers. Why they don't just block this traffic directly I don't know, but hey, now I can block it. The exception being if the connection has been authenticated as one of my users.
I check all three lists now through their "Zen" list which is a combination of the 3 lists. I seem to be getting a better SPAM/HAM ratio through these 3 lists than I was from Spam Assassin, without having to go through the data stage of receipt :)