Also, no one has mentioned what the title of the song has to do with the meaning of the song, which is usually the most important part behind its message. IOU goes along with the anti-passive message she is trying to convey. An IOU is your word that you will eventually pay someone back or eventually do something about whatever it is you owe. She is saying she will eventually do it, but I think she is more advicating doing the IOU, NOW.
Also, no one has mentioned what the title of the song has to do with the meaning of the song, which is usually the most important part behind its message. IOU goes along with the anti-passive message she is trying to convey. An IOU is your word that you will eventually pay someone back or eventually do something about whatever it is you owe. She is saying she will eventually do it, but I think she is more advicating doing the IOU, NOW.