“If your site is identified as hosting copyrighted material, you’d find your online advertising networks like AdWords disabled, payment facilitators like PayPal would be banned from doing business with you, and search engines would be ordered to take down links to your site (can you feel the SEO earth shaking beneath your feet?). Internet service providers would block access to your site and your domain name would be taken down with DNS blocking –you know, the thing they use for the Great Firewall of China?
Now before this, there was the Safe Harbor provision as part of the DMCA of 1998, which basically prevented sites from being held accountable for the content users post. It’s why YouTube can still exist today – if a user posts infringing content, it’s the user’s fault, not YouTube. But SOPA and PIPA would change that.”
(From B2C) Read more here.
This is what Wikipedia and Google, among other leading sites, looked like today: