If enacted, either of these bills will create an environment of tremendous fear and uncertainty for technological innovation, and seriously harm the credibility of the United States in its role as a steward of key Internet infrastructure. Regardless of recent amendments to SOPA, both bills will risk fragmenting the Internet's global domain name system (DNS) and have other capricious technical consequences. In exchange for this, such legislation would engender censorship that will simultaneously be circumvented by deliberate infringers while hampering innocent parties' right and ability to communicate and express themselves online.
Read the entire Letter at eff.org.
Here's an excellent article on the topic: Don't Break the Internet published by the Stanford Law Review On-Line.
Directing the remedial power of the courts towards the Internet’s core technical infrastructure in this sledgehammer fashion has impact far beyond intellectual property rights enforcement—it threatens the fundamental principle of interconnectivity that is at the very heart of the Internet.
Court-ordered removal or replacement of entries from the series of interlocking databases that reside in domain name servers and domain name registries around the globe undermines the principle of domain name universality—the principle that all domain name servers, wherever they may be located across the network, will return the same answer when queried with respect to the Internet address of any specific domain name. Much Internet communication, and many of the thousands of protocols and applications that together provide the platform for that communication, are premised on this principle.
Indeed, this approach could actually have an effect directly contrary to what its proponents intend: if large swaths of websites are cut out of the Internet addressing system, those sites—and the users who want to reach them—may well gravitate towards alternative, unregulated domain name addressing systems, making it even harder for governments to exercise their legitimate regulatory role in Internet activities.