There has been considerable discussion on some of the blogs I frequent of the view of Alex Tabarrok that, for someone who believes in God, doubting evolution is rational. Pharyngula, among other commentators, correctly points out that the existence of God wouldn't change any of the evidence we have in favor of evolution, so if we had conclusive evidence of God's existence, we ought to believe in both God and evolution.
I suspect that Tabarrok's mistake is an instance of a common error one encounters among those examining theistic hypotheses. He seems to radically over-estimate the explanatory power of simply postulating God's existence. The same mistake is made by those who suggest that God is a simpler explanation of any given phenomenon than an alternative scientific explanation. Unfortunately, God's existence on its own has minimal explanatory power. In order for "God exists" to explain anything, a supporting theological framework is required; we need theories about the intentions of God, and how those intentions would be fulfilled by the phenomena observed. Absent a framework which explains why God would want the species we observe, evolution is still the best explanation for why we see the species we do.
The need for the theological framework also ruins the theory that God is a simple explanation. I do not know of a theological framework of that kind which is remotely adequate to explain the world we observe. In the absence of an example to examine, it is impossible to judge with confidence whether a theological framework comparable in explanatory power to our best atheological theories would be simpler or more complex. Still, there's a slight reason for expecting it to be more complex rather than simpler, since it will have to include at least one significant additional entity (God, obviously).