In case you haven't seen it yet, there is a new paper in J. Neuroscience that reports the existence of mirror neurons in human inferior frontal gyrus (~Broca's area). It used a repetition suppression fMRI paradigm and found a suppression effect (different > same) both when subjects executed and then observed the same action and when subjects observed and then executed the same action. This appears to be the best evidence yet for the existence of mirror neurons in humans: an effect was found in both directions, execute-->observe & observe-->execute, and it is showing up in the right place, Broca's area, the presumed human homologue of monkey area F5. Another thing I like about this study is that it used object directed actions rather than pantomime which makes it more comparable to the monkey studies.
I haven't yet read the paper closely. I'd be very interested to hear what folks think, so please post a comment. My only general concern is with the repetition suppression effect itself. We've used it previously and it strikes me as a bit on the sketchy side. The effects are very subtle and susceptible to the boredom critique: the suppression effect is not neural adaptation but instead reflects the fact that the subject is bored with the repetition of stimuli and therefore allocates less attention for same trials versus different trials. I'm not sure this critique applies here though given that the same trials cross modality. I'll have to think about that one.
Kilner, J., Neal, A., Weiskopf, N., Friston, K., & Frith, C. (2009). Evidence of Mirror Neurons in Human Inferior Frontal Gyrus Journal of Neuroscience, 29 (32), 10153-10159 DOI: 10.1523/JNEUROSCI.2668-09.2009