My wife is hooked into the county extension office. She sent me this link a ways back about mowing height...
I cut mine at 3.5" in the summer. I'm not big on watering my grass (i.e. I don't) so I try to let it provide its own shade.
The spring I'm at 2.75" and then in the fall, I step-wise lower it down to 2" so the leaves blow into my neighbors yard