• A police officer has stopped a car for speeding, while the officer is writing up the citation, another officer runs a dog around the outside of the car to sniff it.  If the dog alerts to the car, the officers have probable cause to search and can do so without a warrant.
• Officers have set up a drunk-driving or license checkpoint where every car is stopped.  While one officer checks ID's another can have a dog sniff every car.
• An officer has an anonymous tip that there are drugs in a residence.  The officer can bring a dog for a "knock and talk" encounter.  If the dog alerts to the house the officer can secure the residence while other officers go get a warrant.
• Dogs can be used to randomly sniff luggage checked at airports.
• Dogs can be used to sniff cars waiting at stoplights.

The decision is not surprising since the court has been friendly to dog sniffs in the past.  Since I generally resent government intrusion on citizens I am wary of the idea that there is no legitimate expectation of privacy in illegal activities.  It sounds too much like, "if you have nothing to hide there is no reason object to a search."

On the Volokh Conspiracy, Owen Kerr asks:

Can the police send a computer virus to your computer that searches your computer for obscene images, or images of child pornography, and then reports back to the police whether such images are on your computer — all without probable cause, or even any suspicion at all? The traditional answer would have been no: the police cannot enter your private property to search even for non-private stuff. But thanks to the increasing focus on the nature of the information rather than how the information is obtained, it's no longer so clear.

Unleash the hounds (Arbitrary & Capricious), Hoakum! (Grits for Breakfast)

Update:

A different view of my DWI checkpoint hypo: If officers walked a drug dog around all vehicles initially stopped at a DWI or license checkpoint (in contrast to walking a drug dog around a car after the driver had been lawfully detained at the checkpoint for further investigation for a valid reason), then a court would likely rule that the primary purpose of the checkpoint was drug detection, not DWI or license checks. In City of Indianapolis v. Edmund, the court ruled that traffic stops with the primary purpose of drug detection were unconstitutional.  (This take is from Robert Farb, a professor at the N.C. Institute of Government)

It is possible or maybe likely that a court would rule that use of dogs at a DWI checkpoint shifted the primary purpose of the stop from drunk driving to drug interdiction.  How does a court judge what the primary purpose of a checkpoint is?

• Federal Sentencing Guidelines Lite.  "All the complexity, confusion and uncertainty of the Federal Sentencing Guidelines but without the annoying Sixth Amendment problems."  They're fizzy and yellow, but likely to make Congress gag and leave a bitter aftertaste for defendants who still face longer sentences.  By making the guidelines advisory rather than mandatory, the court has eliminated a provision that was central to what Congress tried to accomplish, reducing or eliminating disparity.  So for judges who follow the guidelines defendants will still face increased sentences for facts not found by a jury or proved beyond a reasonable doubt.  This was the principal problem the 5-justice majority had with the guidelines.

• The Crime Pyramid.  The guidelines are now merely "advisory."  Kinda like the food pyramid.  This should enjoy the same success as the food pyramid has in eliminating obesity.  Maybe judges could end every sentencing with "and would you like some supervised release or probation with that?"
• It's the Real Offense. The Sixth Amendment problem with the Guidelines is in the "real offense" versus the "charged offense."  Early on the Sentencing Commission picked the real offense approach and has been wedded to it ever since.  The real offense approach is this: no matter what the prosecution charged you with and what the jury convicted you of, a probation officer will find what it is more likely than not that you "really" did and that is what we will sentence you for.  The Sentencing Commission has extremely bright people, but the system it came up with had serious problems and from the very beginning was far too complex.  Imagine that we had sent the Founding Fathers to Philadelphia and instead of the Constitution, they came out with the Internal Revenue Code.  That pretty much sums up the work of the Sentencing Commission.
• Judicial activism?.  The anti-guideline opinions have so far been bulletproof when it comes to claims of judicial activism, because icons of the right Justices Scalia and Thomas have been the bought wholeheartedly into the Sixth Amendment interpretation, along with Justice Stevens.  In some ways the guideline fixers, led by Justice Breyer are the real activists because they are desperately trying to find a way to preserve the status quo, even though a majority has clearly ruled that the status quo is unconstitutional.