SOPA stands for Stop Online Piracy Act, which it will not do. What it will do is require ISPs to block access to content which allegedly infringes upon copyrights when requested to do so by the holder of said copyright. It will also require Visa, MasterCard, PayPal, et al to block fund transfers to individuals or groups trading in content which they allegedly do not own.
The real non-technical problem here is that these blockages won't require a court order or a warrant. The copyright holder simply has to make a claim of infringement.
Also, if this wasn't bad enough, it'd make streaming copyrighted material a felony.
There are a lot of technical problems with this too. The ISP will probably just poison their DNS servers to prevent the site in question from resolving. There isn't a lot to keep someone from just using a DNS server located outside the United States, or just turning up their own resolver for the matter. If actual routes were blocked, proxy servers aren't exactly hard to find.
As far as blocking financial access, this is yet another reason why I like Bitcoin.
There is no third party intermediary, you just send money and be done with it.
In conclusion, SOPA is a bad law that will make it hard for ISPs to do business. Lamar Smith (the bill's sponsor) should go fuck himself with a garden rake, and I do not mean with the handle.
On a more pleasant note, despite my better judgment I decided to dig around on the CB band (27 mhz) tonight. Someone is playing a little Casio keyboard tune on CB channel 17.