Hmmm...I don't know if it signed you up for spam or not. I mean, if a particular person wanted to spam users X, Y, and Z, they would just have to @reply them all the time or something. Just being on Twitter makes you susceptible to that. I don't know if "Twitter spam lists" exist or not (it's certainly possible).
As for the site, it's impossible to say whether it hosted malicious content or not without checking it out myself.
For future reference, you can check the location (aka "long link") of a bit.ly link by adding a plus (+) to the end (example: http://bit.ly/900913+