This seems to be a rather contentious issue lately. One recent thread involves a critical paper by Lotto, Holt, & Hickok in TICS, a commentary on that paper by Stephen Wilson, and a response to Wilson. What I like about this thread is that it basically leads to an agreement of viewpoints. Lotto et al. argue that mirror neurons are not a viable instantiation of the motor theory of speech perception. Wilson points out that the motor system plays a top-down role in speech perception (which is different than saying that it is where speech perception happens). We agree completely with Stephen but emphasize that the motor system's role appears to be fairly small. Stephen discusses some interesting data in his commentary and makes a coherent argument. It is definitely worth a look. The other nice thing about this thread: it's nice and short.
Hickok, G., Holt, L., & Lotto, A. (2009). Response to Wilson: What does motor cortex contribute to speech perception? Trends in Cognitive Sciences DOI: 10.1016/j.tics.2009.05.002
Lotto, A., Hickok, G., & Holt, L. (2009). Reflections on mirror neurons and speech perception Trends in Cognitive Sciences, 13 (3), 110-114 DOI: 10.1016/j.tics.2008.11.008
Wilson, S. (2009). Speech perception when the motor system is compromised Trends in Cognitive Sciences DOI: 10.1016/j.tics.2009.06.001