maximillianos - 5:25 pm on Jun 27, 2011 (gmt 0)
Run a crawler like LinkSleuth over your site. It may turn up some bugs in your code that is incorrectly building links on pages that you never notice.
This happened to me, and the result was hundreds of thousands of garbage pages being indexed by Google through bad links that were not even visible on the page (no link text) due to a bug.
I thought the same thing as you, it must be a bug with Google, or some other site linking to me wrong... but in the end the errors were in my own backyard!