I was surprised by the pick of Harriet Miers to take O'Conner's seat, but after watching the reaction from the Left and Right, I have developed a theory.
Suppose Bush wants a quick confirmation, he goes with someone that Harry Ried and others are willing to accept. No fuss, no muss, and his bud who is the White House Counsel gets rewarded for years of diligent service.
Now, suppose that the Democrats decided to object to her. A certain amount is to be expected, because they are playing to their base. But if anything comes up to call the confirmation into question, Bush digs in, ala Bolton, Rogers-Brown and Owen. Then, because of lack of support on the Right, and opposition on the Left, Miers withdraws, and Bush goes with a Luttig.
He can offer that he has made an effort at consensus and was rejected. Therefore, screw you, here comes the hard core.
Okay, maybe too complicated, but that is what I have to do for a living, think about what else it could be.