] This Act may be cited as the `Controlling the
] Assault of Non-Solicited Pornography and Marketing Act of
] 2003', or the `CAN-SPAM Act of 2003'.

I'm not sure if this was blogged here before. In addition
to prohibiting sending SPAM, it also expressly (sec 6) prohibits
you from promoting your business via spam, i.e. if you hire
spammers, you're also in violation of the act. This seems like
it could be a more fruitful avenue of enforcement -- prosecute
the end-users of the "spam service" rather than the spammers
themselves.

CAN-SPAM Act Text