"What's a blue slip?"
If two senators from a given state (I think two is required now- at various times it's been only one required) object to a judge from their state, that judge never sees the light of the Judiciary Committee. A senator's making that objection is called using the "blue slip."
It's a real problem in places like California or Michigan with 2 democratic Senators. Bush really has to curry favor with them in advance and he'll usually have to nominate more moderate Republicans than he would otherwise.
There is a commission that recommends judges in CA. We've had some real lightweights come out of that process.
The blue slip is a tradition, not a rule such as 60 votes for cloture, and it is even more undemocratic than the filibuster. I can't believe that the Senate Judiciary Committee in which the GOP has a 2-vote advantage would refrain from voting a judicial nominee to the floor merely because two liberals from Michigan object that Bush didn't nominate a young John Conyers. If we had Jon Kyl as Chairman instead of Arlen Specter, Kyl would tell Levin and Stabenow where they can stick their blue slips.
And if the GOP needs to betray Henry Saad (a third judge being blocked by Stabenow and Levin) just so that two judges who weren't even being filibustered can get a vote, then the Senate is in even worse shape than I thought.