This is a BBC 60-minute documentary where Alastair Sooke explores the stories behind the world's most expensive paintings including works by Rothko, Monet, Bacon, Rubens, Klimt, Freud and of course Picasso. Its a fascinating trail of discovery into the super rich buyers, and what drives the art market. Along the way he finds that what makes art valuable (apart from their intrinsic worth and having being painted by famous artists) is "provenance", i.e. a kind of lineage of the previous owners or history associated with the work.
I actually think that art at this level is a kind of currency for the super rich. I highly recommend this documentary.