I just noticed Rob Neyer's column on Toronto moving to a four man rotation. Actually, Rob's article is more about the criticism of the move being based on incorrect facts. Good for Rob for calling people on that. He also points out the following:

Last August, my friend Rany Jazayerli wrote a compelling three-part series of articles about the four-man rotation and why it deserves to make a comeback. I urge you to search out Rany's original pieces, but let me summarize: 1) Pitching on three days' rest is not more likely to lead to injury than pitching on four days' rest, and 2) pitching on three days' rest does not result in less effectiveness than pitching on four days' rest (and in fact there are many who think it might result in greater effectiveness).