I've been reading a collection of essays by the late (and really rather brilliant) David Foster Wallace recently, and he made this aside on the relationship between advertising and art:
"The reason why even a beautiful, ingenious, powerful ad (of which there are a lot) can never be any kind of real art: an ad has no status as a gift, i.e. it's never really for the person it's directed at"
Even given the current vogue for "participation" (flashmobs, crowd-sourcing, social media campaigns etc), I still think he has a point: while our industry is better at making people feel engaged and involved with our campaigns and brands, and is increasingly focussed on creating cultural capital (not just mental spam), we are still ultimately doing it for our client, not the public (not that there's necessarily anything wrong with that).
PS -if you haven't read "Infinite Jest", I suggest you take a couple of weeks off and do so