I like iTunes, I like it a lot. However, if you are using the ‘Add to Library’ function to add an entire directory to iTunes, and that directory also contains a playlist (.m3u file) it will also add every song listed in the .m3u.
This results in all the songs from a given directory being added twice (if the .m3u has a line for each song, which is common). Why this was ever considered a behavior that would be desirable I have no idea.
Yea, it took me quite some time to figure that out because I didn’t realize some of my folders has play lists in. It is a pain in the keister. After about 20 times, you will actually remember that it happens and you will be fine. And yes, itunes is one darn god program, as is most things apple.