If the point of copyright law is to stop people from using copyrighted material it is very effective. If there is some other point, than maybe not. Copyright law is so strict that it is hard to use certain copyrighted works even it what seems like acceptable and fair use.
In this era of internet and international, it's nearly impossible for America's copyright laws to be effective. Individuals post whatever they want on the web, without regard to creative ownership, leaving it up the creator to chase down any infringement. People in China reprint art and books as they wish, and the government doesn't stop them. Laws are only effective if everyone agrees that they are fair and enforceable.
I don't think that America's copyright laws are very effective, especially in today's crazy technological age. IT is just too easy to share information and to steal ideas from other people, especially online. I think that people would think twice about violating copyright laws if consequences were steeper and more serious.
Fair use and copyrights have been thrown around a lot lately. People on Youtube have had their videos taken down and their revenue taken from them through unfair DMCAs even when the person creating the content didn't include any part of the original content in their videos. A lot of this probably comes from people who want to abuse the system to get what they want and an amount of policies that can be abused.