I found out what has happened. XRumer 5.0 was released which supports advanced Captcha defeat including Gmail. I knew it'd happen eventually but it's pretty obnoxious when you have multiple sites that all start getting nailed.
Here's a slashdot article that talks about it. I switched my forums to recaptcha as it doesn't seem to support that at the moment but I think we're in for a serious cat and mouse game.
http://it.slashdot.org/article.pl?sid=08/10/02/1415205