For the basic purpose you originally stated... Dropping a folder onto the player and not having it add the old tunes twice... wouldn't the file size and tag data be enough of a check to ID it as the same song?

Hmm, but then that wouldn't cover the bitrate-upgrade situation... And it wouldn't cover poor tagging practices... Hmm the soundprint stuff is looking better all the time, isn't it...

Didn't someone here on the BBS actually work on a soundprint application that went opensource, and we did a whole thread on it?