Web content theft is rampant, because for most thieves, the consequences aren't too dire. They get discovered, you send a cease & desist letter, and they probably take down the stolen material. I'm not a lawyer, but it's my understanding that it's hard to sue them and get monetary compensation because you have to prove they harmed you financially.
You might try surfing the boards at
www.webmasterworld.com - this topic comes up regularly and people have good advice for how to handle it.