I wonder how things go if you challenge them in court. This is surely a topic for another list, but it seems to me it'd be fairly difficult to prove unless they downloaded part of the movie from your IP and verified that what they got really was a part of the movie.
I have the netflow records to prove this is NOT the case. All MediaSentry (et.al.) do is scrape the tracker. We have also received a number of takedown notices that have numbers transposed, involve parts of our netblock that were not in use at the time in question, etc. I would think that whole "penalty of perjury" thing would have some weight behind it. Stanford (in)famously managed to get DMCA notices for all the printers on campus, just by faking a client into putting the printer's IP into the tracker as a seed. Cheers, Michael Holstein Cleveland State University