There are relatively few other companies on the list the average internet (power) user can boycott effectively. How am I supposed to boycott Nike or Reebok? I buy shoes like once every two years. Should I write an angry blogpost a year or two from now when I pointedly buy a non-Nike shoe?

(As an aside, why the hell are Nike or the Ford Motor Company supporting SOPA? Is it one of their subsidiaries, or just corporate solidarity?)

An effective boycott needs to be noticeable, and that means either terminating a subscription or stopping an extremely regular (daily or weekly, perhaps monthly if it's substantial enough) purchase. The only other company on the list which seems vulnerable to that sort of boycott -- unless there are far more people picking up something weekly from Tiffany's than there should be -- is Time Warner. Terminating your cable service is a very immediate, noticeable act. If as many people terminated their TWC service as transfered domains away from GoDaddy, I think it would make some headlines.

Of course, internet service is pretty screwed up in most markets. Many people don't have a choice of (high-speed) internet service provider at all, so protesting TWC probably requires turning off your internet entirely, which is pretty hard to manage. So really, GoDaddy is probably the only company on the list which can be effectively boycotted.