Well I don't think I disagree with that, and I'm sure W is judging her on her professional demeanor. But we all know that as soon as a person gets onto a place like the Supreme Court where no one can force you to be accountable to anybody, there's a big temptation to let your whims have rein. Blackmun, Kennedy, Souter, and others all started out as reasonably conservative in their first year, just as they appeared to others before confirmation, but with no one to answer to they all soon enough discovered the bleeding heart that was always within them.
The danger in a nominee like Miers is that there's no evidence she's thought deeply about why she's a conservative, what it means to be a conservative, or what any of that means when it comes to interpretation of the constitution. With someone like her, there's a big danger that her personal beliefs are all that matter. There is no reason to think she has any objective philosophy of jurisprudence to fall back on.
I don't know about you, but I don't want someone making decisions based on what they "feel" about a given situation. I want them making decisions based on the law, what it actually says, what the original intent was. The consitution is a very short document. It doesn't take a law degree to understand it, but it does take a good mind to understand the babblings of the various lawyers who present their case. I don't want someone basing a decision on which lawyer made the best "legal" case, I want it based on what the constitution says about how it applies in this situation.
Track record means nothing. Character and judicial philosophy mean everything. W knows those things about her, we won't until the hearings. Of course, that is provided the committee actually asks questions instead of expounding on their favorite issue for ten minutes until their time is up and the next one starts pontificating.
Who knows, maybe one of the best things that will come out of this nomination is that the judiciary committee will actually begin to ask questions again.