We'll be joining the SOPA blackout tomorrow
I've written some about this issue in my blog at Free Software Magazine:
"Piracy is not a problem; SOPA is not a solution"
But some of the best arguments (IMHO) have been posted by Tim O'Reilly:
Tim O’Reilly: Why I’m fighting SOPA
SOPA and PIPA are Bad Industrial Policy
From the EFF:
How PIPA and SOPA Violate White House Principles Supporting Free Speech and Innovation
Techdirt has written a lot about SOPA/PIPA.
A good source on what you can do about SOPA/PIPA is American Censorship.

