VERY doubtful.

1) Like Jose said, they wouldn't make mp3 players if they were against mp3s.

2) It's blatant invasion of privacy.

3) It would cost them millions to hack into individual computers one at a time to locate mp3s.

If it happens, the person being sued could easily counter sue for invasion of privacy and exploitation (due to the fact they provide mp3 players to the public.)

I'm going to jump on this and say it's definately not happening.

Plus, if they did sue, they could only sue for mp3s of artists on their record label. And that doesn't include Ayumi.