The article on agilepanda is well written but the site at http://americancensorship.org/ focuses on website blocking, jail time if you "stream a copyrighted work" and the very general threat of "Chaos for the Internet". It's the wrong approach IMO.
The decision makers, or our target market for this if you'd prefer, are congress, the senate and the president. There's an election coming up and we have real power we can wield. So here's my suggestion:
1. Make it crystal clear that replacing the DMCA with SOPA will kill many of the job creation machines coming out of Silicon Valley and the rest of the USA. It will prevent the creation of new businesses like Facebook that can only exist through user generated content and who generate billions in tax revenue and jobs for the US economy. If a representative supports this bill they are making it clear they don't support job creation in the USA.
2. Make it clear that this is not about online piracy, but about government control of a free communications medium. It is tantamount to the US government taking control of the country's newspapers and having the ability to selectively block the publication of editions they don't approve of.
3. Call your local congressman and senator and let them know that if they support SOPA, they don't support job creation in the USA and they oppose freedom of communication. Let them know two things: If they support SOPA you will not vote for them and you will encourage everyone you know to do the same. Secondly, let them know you will contact every major political donor in the area and make them aware of the representatives stance on the issue and how it endangers American business and innovation.
If we simply "protest" by shutting down our websites or sitting in the street, we risk getting lumped with the Occupy movement. However you may feel about that, what our politicians are most afraid of is losing their jobs and losing their funding. So lets hit them where it really hurts and take the power back.