Working at UCSF has taught me a lot about academic medicine.
1) Pay is less. Not bad, but not as much as if you were in private practice.
2) Teaching duties abound. In charge of residents, med students, etc. on floors.
3) Most I believe do clinical or basic science research.
4) Not much free time as was previously posted on this thread. I only work with Anesthesiologits, so this might be biased. Academic medicine is demanding.
5) Some specialties, for instance Rheumatology, give you ample time for research. At Stanford, Rheumatology fellows and faculty, typically are in clinic 4-8 hours per week, but are heavy researchers, so they spend more time in the lab.
6) Most of these may be different depending on the institution or program you are in, but I thought this may give you a general idea of what goes on in academic medicine.