Boing Boing’s Cory Doctorow summed it up rather succinctly:

Boing Boing could never co-exist with a SOPA world: we could not ever link to another website unless we were sure that no links to anything that infringes copyright appeared on that site. So in order to link to a URL on LiveJournal or WordPress or Twitter or Blogspot, we’d have to first confirm that no one had ever made an infringing link, anywhere on that site. Making one link would require checking millions (even tens of millions) of pages, just to be sure that we weren’t in some way impinging on the ability of five Hollywood studios, four multinational record labels, and six global publishers to maximize their profits.

Fight For The Future