I agree with the many commentators on all sides who think it's inappropriate for President Bush to be pushing Harriet Miers' Christian religious views as a motivation or argument for placing her on the Supreme Court. In theory. As Largo from Type R Caston wrote, religion should be irrelevant for an ideal nominee.
I do not consider it much of a stretch to conclude that by selling a nominee based on their religious views, that one has hopes in seeing those views come into play during their stay on the court.
Personally, I could care less what Mier’s believes, she could be a Zoroastrian Communist for the clubbing of baby seals with tire irons and I could support her provided I was to believe that she would be a good steward of the Constitution. The point here is that a person’s views are irrelevant when a Justice on the high court is performing their duties as originally conceived by our founding fathers.
Unfortunately, there are no "ideal" nominees, there are only nominees who hide their ideological biases and nominees who reveal them. One of my biggest criticisms of both recent Supreme Court nominations has been that the nominees have had very little "track record" -- apparently this is seen as a virtue by some politicians, but most of us would like to know more about the people whose rulings we'll be subject to for the next several decades. (As everyone knows, the courts have become political despite the life tenure of judges, which was intended to reduce the politicalization.)
Knowing that Miers is a conservative Christian is a piece of her track record. I'd really prefer if she had written extensively on, oh, let's say Constitutional law before being nominated, but I guess we'll have to extrapolate what we can from what she has revealed. The President wouldn't have to play up Miers' Christianity so much if he had nominated a person with more relevant credentials, but given Miers' background it's hard for me to identify any aspect of her behavior that will help us predict her future more accurately than will her Christianity. So, since that's all there is, it's rational for her religion to be the focus.
Based purely on my perception of history and on religious stereotypes, Catholics seems to make good justices, and I bet Jews would also. There haven't been many (any?) conservative Christian justices, but based on my own perception of the group I think that a conservative Christian nominee is likely to do a better job interpreting the Constitution properly than would a Zoroastrian Communist. Most of the Christians I know are honest, hard-working and sincerely interested in the welfare of others. Those Christians I know who are intelligent are also intellectually honest, consistent in their views, rational, and able to make hard decisions that conflict with their preferences. One of the tenets of Christianity is that we make decisions based on what's in the Bible and not on our own selfish desires, and the principle of applying the Constitution literally and faithfully is very similar. Furthermore, a well-read Christian will have an important perspective on the context our framers lived in that may not be readily available to those of other backgrounds.
So, while I know very little about Harriet Miers personally, I know a lot about one of the groups she belongs to, and from that I can infer some important bits of information. These inferences are not nearly as useful as if she had written about such matters herself, but I hope they illustrate that Miers' selected religious affiliation can tell us something about how she might behave in the future.