It's not just a question of legal/illegal. Some things that are illegal are not criminal--they create civil liability instead. If you lose, you owe money but you don't go to jail or have a criminal record.
Have any individuals been criminally prosecuted for their personal BitTorrent use? I've read a lot of stories of people being sued, but I can't remember a story of criminal prosecution. I guess it would be possible if the prosecutor could make the case that BitTorrent is a form of distribution, and the amount meets the criteria in the law:
http://www.copyright.gov/title17/92chap5.html#506