I agree that the PIN is probably rarely used, partly because there is no automated way to use it. If I used it I would probably do something like three digits for the artist and two for the track.

But, considering it is rarely used, wouldn't it be nice for "search by title" to be the first search option rather than pin. Pretty much every passenger I've shown how to build a playlist by searching has subsequently wiped it out at least once by hitting menu three times instead of search three times.