It would be truly amazing to see this. Reddit going dark is fantastic, but to an extent it's "preaching to the choir"- Reddit is already the centre of SOPA activism.
Google, Facebook or Twitter going dark would be a huge statement. Is there a movement for other sites to go dark on Jan 18th as well? My startup going dark by itself wouldn't have a huge impact, but if it was part of a national day of activism it could be great.