Ganked from the Save the Internet website:

"Isn't the threat to Net Neutrality just hypothetical?

No. So far, we've only seen the tip of the iceberg. But numerous examples show that without network neutrality requirements, Internet service providers will discriminate against content and competing services they don't like.

-In 2004, North Carolina ISP Madison River blocked their DSL customers from using any rival Web-based phone service.
-In 2005, Canada's telephone giant Telus blocked customers from visiting a Web site sympathetic to the Telecommunications Workers Union during a labor dispute.
-Shaw, a big Canadian cable TV company, is charging an extra $10 a month to subscribers in order to "enhance" competing Internet telephone services.
-In April, Time Warner's AOL blocked all emails that mentioned www.dearaol.com — an advocacy campaign opposing the company's pay-to-send e-mail scheme.

This type of censorship will become the norm unless we act now. Given the chance, these gatekeepers will consistently put their own interests before the public good.

Won't more regulations harm the free Internet? Shouldn't we just let the market decide?

Writing Net Neutrality into law would preserve the freedoms we currently enjoy on the Internet. For all their talk about "deregulation," the cable and telephone giants don't want real competition. They want special rules written in their favor.
Either we make rules that ensure an even playing field for everyone, or we have rules that hold the Internet captive to the whims of a few big companies. The Internet has thrived because revolutionary ideas like blogs, Wikipedia or Google could start on a shoestring and attract huge audiences. Without Net Neutrality, the pipeline owners will choose the winners and losers on the Web.

And when the network owners start abusing their control of the pipes, there's nowhere else for consumers to turn. The cable and telephone companies already dominate 98 percent of the broadband market. Only 53 percent of Americans have a choice between cable and DSL at home. Everyone else has only one choice or no broadband options at all. That's not what a truly free market looks like. "