I don't think all spammers are using copyright material [1] to avoid Bayesian filtering. I received some today that are using public domain material—one using a section from Jack London's White Fang (and funnily enough, trying to get me to refinance Condo Conner, which I sold last year! [2]—okay, okay, I lived there for 14 years but still, you'd think they could update their information) and another one using a section from Rudyard Kipling's Rikki-tikki-tavi [3] (which is yet another one trying to get me to refinance Condo Conner).
But then I get another one, this time quoting from an essay about Bill Gates [4], so there is still hope of getting DMCA (Digital Millenium Copyright Act) on their ass …
[3] http://www-2.cs.cmu.edu/afs/cs.cmu.edu/usr/mongoose/www/rtt.html