I did, and I loved it. The film is based on Martin Sixsmith's book of the same name and, given that the book is almost always better than the film, I snapped it up when I spotted it in a Waterstones two for one offer recently.
If you're unfamiliar with the story, Philomena the film follows Irish pensioner Philomena Lee (Judi Dench) who enlists the help of cynical journalist Martin Sixsmith (Steve Coogan) as she attempts to track down the son that she, then an unwed teenager, was forced by the Catholic Church to give up as a baby. Philomena the book is the story of that baby.
It's a remarkable story too. Antony Lee, rechristened Michael Hess, was adopted by an American family, moved across the Atlantic, excelled in school and university and went on to a successful career as a lawyer, eventually becoming Chief Counsel to the Republican party. Michael Hess was also gay, had a crippling need to fit in and be accepted by the establishment and died a grisly death from AIDS.
The themes of 'outsiderness' and the psychology of being adopted are given a really interesting exploration in this book. Michael's need to fit in is desperately sad and the fact it leaves him working for a government who are actively blocking funding for AIDS treatment at a time when he is dying of it is the most awful logical conclusion of that need. It makes for a great narrative as well - one of those great biographies which is as good as any fictional stories you'll read.
I don't think you need to have seen the film to enjoy the book. Nor do you need to have read the book to enjoy the film. The film is essentially the story of the book being written, so it is genuinely interesting to look at them as companion pieces. Michael isn't a character in the film - we're shown Philomena searching for him in America, but she arrives far too late and he's already dead. On the flipside, Martin Sixsmith himself is only fleetingly a character in the book (and then only to explain his research at the end of each section) whereas in the film he looms large.
The other major difference I found between the two is that the sense of anger at the Church that pervades the film is absent from the book. In the film, it's the character of Martin who brings this in; Martin the author does not. I think this is probably for the best - the story of Michael Hess is much more interesting than just a rant against the Catholic Church in Ireland. And frankly if you can read this book and not get angry at the Church then I question your understanding of the story. It doesn't need to be reinforced.
So if the book better than the film? I'm not sure. Both are equally good at telling different aspects of the same story and as such both are worth your time. The film is out on DVD now so pick up the two when you next have a free weekend. Go on treat yourself. You deserve it (probably).