To be fair, Miers has been a successful lawyer for many years now. She's just never had any judging experience.
Miers was a terrible pick for BOTH ends of the political spectrum. The Republicans distrust her because they don't know too much about her. The Democrats wouldn't trust anyone President Bush selected, but their problem with her is much the same: unpredictability. The only one who knows for sure what kind of decisions she'll make is Miers herself, because she has no judging record.
Personally, I'm a tad worried that she's a born again Christian. The Supreme Court, with its life appointments, is no place for someone who will base decisions on national policy for all 300 million Americans by their religion.
Also, abortion is not really that important a topic in the long run, in terms of "things the Supreme Court needs to concern itself with." There are more important things to worry about, like whether Miers would be willing to allow torture of Iraqi POWs, or whether she would influence a Presidential election, like the Supreme Court did to Al Gore in 2000. (By the way, in 1989, I believe it was, Miers answered a questionnaire on abortion saying she would be perfectly willing to ban it in all cases, including cases of rape and incest, except when the mother's death is imminent.

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We'll see what the future holds, but I'm personally not really liking what I'm seeing. Let's hope Bush doesn't have to appoint any more justices.