Ok, I did this (I called the file directory.blacklist.txt, added a . , enabled blacklists (after disabling delete blacklisted files!), and it says one pattern loaded (I have a flat directory structure here).
It claimed to have loaded one rule, but did not blacklist any songs (the duplicate detection did work, however).
Unless I'm missing something, this will only work so long as the files exist in this directory, however. My goal was to be able to move them off the PC, and have it save a list of what was downloaded.
In order to do this, I replaced the contents of my blacklist file with a dir /b on that directory. After this, it loaded 506 patterns, but also failed to blacklist any songs (the extensions were different (I've transcoded mp4 to ogg, but the filenames were exactly the same).
Any idea why?