Article in the New Scientist (subscription required to access full article). Subtitle says it all:
"Copyright laws are designed to encourage creative endeavour. But on the web, they are being used to silence and intimidate."
The article highlights how section 512 of the Digital Millenium Copyright Act (DMCA) enables copyright owners to send 'takedown notices' to ISPs or web hosts without going to court. The onus is placed on the person who posted the materials to legally challenge the takedown notice, meaning most give up and remove the content rather than face expensive legal costs. Takedown notices are becoming an effective form of censorship.
The article quotes a couple of recent studies. One found that 47% of takedown notices concerned material that would likely be deemed fair use. Another found that 9% of takedown notices contained significant flaws that rendered them invalid. Regardless, more than half the content was removed. Interestingly, the majority of notices related to commercial sites run by competitors. Example given was a company that sent 15 takedown notices in 2004 to Google, demanding search results linking to its competitors be removed (the reason given: the web sites contained copyrighted phrases). Google complied and replaced the links with links to the takedown notices archived on the Chilling Effects website.