And for a low, low price, you can tell everybody that this is your song

According to author Bill Scheft, you are allowed to print up to four lines from a non-public-domain song in a book before having to pay for the privilege. (Yes, that means websites that post song lyrics are legally vulnerable.) That number is based on the copies in the initial print run, so if you want to publish, say, a teenager's diary, you'd better make your sales estimate really low on your initial P&L and then pick up a huge audience later.