Nike Beatles Revolution Ad

This ad, which ran several years ago, provoked tremendous controversy due to its use of John Lennon's song, "Revolution."  Do you think it is ethical for an artistic work to be co-opted in this way?  If there are consent issues here, whose consent would be required?  Should there be any limits on what advertising can use, or, in a post-modern age, should everything be viewed as available for appropriation and re-purposing?