A while back I wrote about ScanEye. Viewing it, it shows you which files your IP has downloaded in the past. It was restricted so that you could look at the information for your own IP only. Now you can check every IP or filename you want using BTindex, a DHT crawler. By the way, it provides a magnet link for every entry, too.. Since it's a DHT crawler, in case you don't want your IP or file to show up you have to disable DHT.