Lawrence Lessig has gone out on a limb, stating that his legislative solution to stopping spam will work or he'll quit his job.

As Lessig mentions in his post (assuming you want this much detail), Philip Jacob's The Spam Problem: Moving Beyond RBLs is a good explantion of Realtime Blackhole Lists and why they don't work.

Meanwhile, I'm afraid that the longer we wait for effective spam legislation, the less likely it will be to happen. After all, once the spam kings have enough money to lobby Capital Hill, we'll never see any legislation stopping them, only bills facilitating their growth :)

Link courtesy of this Slashdot post.