Nope...if you don't directly share your collection or a list of what's in it (Kazaa and similar have a "More from this user" feature) you can't be caught.
BitTorrent doesn't have a shared folder. Once you begin downloading a torrent, even at the 1% complete point, the partial file that you have is available for others to download. If you look at the files being downloaded, it will tell you the IP address of the other computers you are downloading from, and what percentage of the complete file is available from that IP address.