Thanks to searching through gritsforbreakfast's blogspot, I found the following information:
The Supreme Court, in deciding Illinois v. Caballes, revealed that police use of drug sniffing dogs at traffic stops doesn't constitute a search under the Fourth Amendent. The argument is that "A dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment." (SCOTUS Blog).
I confess, I agree with gritforbreakfast on this one. It doesn't make any sense to me that, just because you may or may not possess contraband in your vehicle, which I concede is against the law, that your right to be searched with little more than a hunch, and I doubt the police would even need that, is forfeit. It seems to contradict what the Fourth Amendment says, which is: "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
It's hard for me to conceive that there would be occasion on a "routine traffic stop" to have probable cause to search for contraband.
For those who say "well, I don't have contraband in my car, so I don't object to them searching and finding it in criminals' cars," I fear you're missing the point. There is a reasonable expectation of privacy that all people enjoy, and there appears to be a fine line now between searching a car, just because, and searching a house, or a business, or a person him or herself.