It looks like the SOPA blackout day has encouraged many citizens to get out and email their senators to voice their disapproval. If you head over to the US Senate's home page and reach this list of senators, many (if not all) of the "contact" links are currently returning a "technical difficulties" message. There's no evidence of foul play here (Anonymous is even currently under a blackout), and while it could be unrelated to SOPA, there's definitely a lot of major web properties driving visitors to the Senate's site today. Hopefully these issues get sorted out quickly so citizens can continue to make their voices heard.
Thanks to everyone who sent this in!