From what I've seen and read on the Internet, it seems to be around the 60 hour a week mark, about the same as a lawyer who probably gets paid in the early six figures (about 160k USD) or a corperate executive who is probably 50 anyway.
BUT frankly speaking, from what I've heard personally from various doctors (ranging from internal med to dermatology) it's something like 25 hours a week (the lucky dermatologist) to 40 for internal med. Honestly even the various emergency med docs I met told me around 50. Please note that in no way am I implying that my personal experience is representative of the entire medical community, buy it seems as if people like to stretch the truth to shy away competition.