Personally, I'd take vandalism, and having to white-wash my storefront any day, over a government forcing my payment processors to shut me down by fiat. Frankly it's hard to imagine someone I'd sympathize with who wouldn't feel the same way; but if you're that person, now's the time to air reason on the side of order; a few weeks from now the cause will definitely be lost.
However, in the long run I don't think web vandalism is a pragmatic solution to the SOPA mess. Right now we have the opportunity to potentially defeat SOPA through legal, peaceful advocacy. Let's seize that opportunity and exploit it to the fullest before anyone considers engaging in criminal acts as part of an anti-SOPA campaign.
To speak your mind on SOPA, to disassociate yourself from those who endorse it, and to attempt to persuade your representatives are all well within your First Amendment rights. To damage or destroy the property of others toward the same goals is certainly not protected speech and I'd say a great deal of soul-searching would be required before one could justify going that far.
There must be a way to use the public's fear as a way to carry this message. Why can't we fund commercials for each state that list the bill's supporters as trying to censor the Internet? Alternately, why not blackout some of the more important routers in protest? I hate that I'm suggesting we break things temporarily to get people's attention, but, what else is new, right?
The problem is marketing: how do we make people care?
So now you pried my opinion outta me ;)