Which types of businesses would be hit the hardest with SOPA's passing?

I think a lot of companies stand to incur expense and opportunity cost under SOPA/PIPA. A few that immediately spring to mind:

Web ad delivery firms and search companies -- would incur significant costs to scrub "suspect" links from their services;

Web payment processors -- would lose revenue to foreign competitors gaining the business of blocked websites;

Any company with a non-US website (noting that the bills' definition of such is utterly ignorant of the technical issues that complicate that definition) that allows user comments anywhere -- they'd have to scrupulously police comments at their own expense or risk getting their entire sites blocked. I can't imagine how costly this same burden would be to Facebook, Twitter, Redd.it, YouTube, blog networks, and other sites with user-created content.

Any company responding to a bogus infringement complaint by an unscrupulous competitors. Your site would remain blacked out while you fought the issue in court; if you were a young, struggling company without deep pockets, the legal costs and lost revenues could kill you.

The US economy, when the venture community stops funding online-oriented startups here, as they've indicated they would do under SOPA/PIPA (see http://www.booz.com/media/uploads/BoozCo-Impact-US-Internet-Copyright-Regulat... )

The open-source software community: many of their tools can be deemed as "helping” piracy;

Small competitors of big media companies, who could abuse the act (as they have been wont to do using the current DMCA) to crush them.