WHO IS SIENNA MILLER?

I've never claimed to be up on celebrity gossip. In fact, aside from the occasional "They're Just Like Us" spread, I can't stand the gossip magazines. I do check in occasionally with some gossip blogs and always keep an eye out for a good Madonna story or picture of Jared Leto. Even I know that Paris and Nichole have "ended their feud". But I have to ask the following question, who the hell is Sienna Miller? All I know is that she is (or was) Jude Law's wife or girlfriend or something but what has she ever done other than sleep with Jude Law and who cares?