It is notable that only FIVE Democrats (Bayh, Byrd, Johnson, Conrad and Nelson) considered Judge Alito a suitable candidate to sit on the U.S. Supreme Court. Across the aisle, Republican Senator Lincoln Chafee (RI) voted against Alito's confirmation, just to prove he's not a "party man."
For the record, Judge Alito was considered "well qualified" by the American Bar Association, endorsed by scores of sitting judges and lawyers, including many, many Democrats. No one could make the case that Judge Alito was unsuitable for the Supreme Court based on his ethics, his experience, his reputation, his judicial temperament or any other metric traditionally employed in the evaluation of a judicial nominee.
There was a time when Senators considered their role as that of reviewing the President's nominees and vetoing any who were too radical, unethical or otherwise unsuitable for the nation's highest court. From the The Federalist Papers, it can be gathered that the advise and consent power is primarily intended to prevent cronyism. The Republican votes to confirm Clinton nominees Ruth Bader Ginsburg (96-3) and Stephen Breyer (87-9) are notable examples of votes based on qualifications. Senators have NOT traditionally voted based on whether the nominee in question was their preferred nominee. There is little question as to whether Ruth Bader Ginsburg would have been the preferred nominee of most Republican Senators. On the other hand, some have posited that the traditional "consent" role of the Senate is too passive, given the immense importance of the Supreme Court.
By their votes today, the Democrat Senators have tacitly endorsed a new standard of review under the "advise and consent" clause, namely: is this a person I might have nominated if I were the President? It's the difference between asking "is this person qualified?" and asking "is this person preferred?"
Whether or not the Democrats have applied a standard superior or inferior to that traditionally employed (and I think there's a good argument to be made that a more active Senatorial role is justified,) it's my sincere belief that the Democrats, being in the minority as they are, have just made a significant tactical mistake in the longer war over the Supreme Court. Unless and until the Democrats regain control of the Senate (which is likely to be a while,) they've now endorsed a precedent by which Republican Senators can legitimately block a Democrat President's nominees based on whether or not the nominee fits each Senator's personal standard of preference rather than on whether the nominee is a qualified candidate. The Democrat Senators could have held a press conference and announced that they would be voting to confirm President Bush's nominee, even though they had serious misgivings about his choice. In doing so, they would have conceded a battleground they had no hope whatsoever of taking while keeping their powder dry for a fight in real contention.