He'll change, just like he did with Roberts. He's a weasel - he'll say he supports a nominee to sound fair, and then will change his mind.
Plenty of folks on the left are starting to have kittens over this nomination. I suggest you examine their complaints.
The Democrats and Rebublicans in the Senate and Bush have been talking about nominees for a long time. The Democrats (at least the ones in red or red-leaning states) are dying for political cover. They don't want to filibuster. They know the kind of person Bush wants, but they need someone they can vote for without getting their brains beaten out by their base and big donors. Why would Reid come out and immediately express a measure of support? Because he very well might be able to make a quasi-defendable case to his own supporters for confirming her. And if a couple of years down the road she turns out to be a disaster for the left, well he can claim he was fooled (and that's an eternity away, anyway, in political time). And that's politics.