Abba stands to make quite a fortune from the new Madonna hit "Hung Up." That's because the song's trademark riff is a sample from Abba's "Gimme! Gimme! Gimme!," originally from 1979 (and which is now one of the top five downloaded Abba songs in the iTunes music store).

Apparently, securing permission took some work. But that's fine. Abba will rake in the cash from what is sure to be a huge amount of royalties, but it's nice to see each party taking into account the integrity of the other.