It should... but there may be a problem with OS X's file mapping. If you get info on a .torrent file, does Tomato Torrent show up in the "Open With" list? If not, try selecting it manually by choosing "Other..." in that list and then navigating to the application. You might need to enable "All Applications" in the popup box at the bottom of the dialogue. OS X should then associate that file with Tomato Torrent, so double clicking it should open the app.