here's an attempt at a neutral runthrough of Thornton...to illicit your opinionated response (i'll quote alot so as to be true to the court's ruling):

Majority Opinion (Rehnquist wrote it):

In a prior case (Belton), the court "held that when a police officer has made a lawful custodial arrest of an occupant of an automobile, the Fourth Amendment allows the officer to search the passenger compartment of that vehicle as a contemporaneous incident of arrest. We have granted certiorari twice before to determine whether Belton' s rule is limited to situations where the officer makes contact with the occupant while the occupant is inside the vehicle, or whether it applies as well when the officer first makes contact with the arrestee after the latter has stepped out of his vehicle."

Here go the facts:
"Officer Deion Nichols of the Norfolk, Virginia, Police Department, who was in uniform but driving an unmarked police car, first noticed petitioner Marcus Thornton when petitioner slowed down so as to avoid driving next to him. Nichols suspected that petitioner knew he was a police officer and for some reason did not want to pull next to him. His suspicions aroused, Nichols pulled off onto a side street and petitioner passed him. After petitioner passed him, Nichols ran a check on petitioner's license tags, which revealed that the tags had been issued to a 1982 Chevy two-door and not to a Lincoln Town Car, the model of car petitioner was driving. Before Nichols had an opportunity to pull him over, petitioner drove into a parking lot, parked, and got out of the vehicle. Nichols saw petitioner leave his vehicle as he pulled in behind him. He parked the patrol car, accosted petitioner, and asked him for his driver's license. He also told him that his license tags did not match the vehicle that he was driving.
Petitioner appeared nervous. He began rambling and licking his lips; he was sweating. Concerned for his safety, Nichols asked petitioner if he had any narcotics or weapons on him or in his vehicle. Petitioner said no. Nichols then asked petitioner if he could pat him down, to which petitioner agreed. Nichols felt a bulge in petitioner's left front pocket and again asked him if he had any illegal narcotics on him. This time petitioner stated that he did, and he reached into his pocket and pulled out two individual bags, one containing three bags of marijuana and the other containing a large amount of crack cocaine. Nichols handcuffed petitioner, informed him that he was under arrest, and placed him in the back seat of the patrol car. He then searched petitioner's vehicle and found a BryCo .9-millimeter handgun under the driver's seat."

Rehquist then reviews the legal rules that are already in place:
1. scope of a search allowed while arresting someone: "the area immediately surrounding him. This rule was justified by the need to remove any weapon the arrestee might seek to use to resist arrest or to escape, and the need to prevent the concealment or destruction of evidence."

2. As for cars: "We therefore held that 'when a policeman has made a lawful custodial arrest of the occupant of an automobile, he may, as a contemporaneous incident of that arrest, search the passenger compartment of that automobile.'"

So that's where we are with the case called Belton, where the person is arrested after stopped in his car. The question is, does it change things if the person has just left his car when the police initiate contact?

"In all relevant aspects, the arrest of a suspect who is next to a vehicle presents identical concerns regarding officer safety and the destruction of evidence as the arrest of one who is inside the vehicle. An officer may search a suspect's vehicle under Belton only if the suspect is arrested."

(Note that last sentence...it's important to remember, as I did not point out, that this is only about searches incident to arrest, as opposed to merely upon suspicion.)

------
Scalia and Ginsburg concurred, but with these caveats:

In a past case, the court "held that a search incident to arrest was justified only as a means to find weapons the arrestee might use or evidence he might conceal or destroy. We accordingly limited such searches to the area within the suspect's ' 'immediate control' --i.e., 'the area into which an arrestee might reach in order to grab a weapon or evidentiary ite[m].'"
In Belton, the court "set forth a bright-line rule for arrests of automobile occupants, holding that, because the vehicle's entire passenger compartment is 'in fact generally, even if not inevitably,' within the arrestee's immediate control, a search of the whole compartment is justified in every case.
When petitioner's car was searched in this case, he was neither in, nor anywhere near, the passenger compartment of his vehicle. Rather, he was handcuffed and secured in the back of the officer's squad car. The risk that he would nevertheless "grab a weapon or evidentiary itemm] 'from his car was remote in the extreme. The Court's effort to apply our current doctrine to this search stretches it beyond its breaking point, and for that reason I cannot join the Court's opinion.'"

Scalia, though, allows the search via a general notion that cops can search with an evidence gathering interest after a lawful arrest:
"In this case, as in Belton, petitioner was lawfully arrested for a drug offense. It was reasonable for Officer Nichols to believe that further contraband or similar evidence relevant to the crime for which he had been arrested might be found in the vehicle from which he had just alighted and which was still within his vicinity at the time of arrest. I would affirm the decision below on that ground."

-----

Souter and Stevens dissent:

When Belton was decided, Stevens writes, "I was persuaded that the important interest in clarity and certainty adequately justified the modest extension of the Chimel rule to permit an officer to examine the interior of a car pursuant to an arrest for a traffic violation. But I took a different view with respect to the search of containers within the car absent probable cause, because I thought 'it palpably unreasonable to require the driver of a car to open his briefcase or his luggage for inspection by the officer.'"

"The bright-line rule crafted in Belton is not needed for cases in which the arrestee is first accosted when he is a pedestrian, because Chimel itself provides all the guidance that is necessary. The only genuine justification for extending Belton to cover such circumstances is the interest in uncovering potentially valuable evidence. In my opinion, that goal must give way to the citizen's constitutionally protected interest in privacy when there is already in place a well-defined rule limiting the permissible scope of a search of an arrested pedestrian. The Chimel rule should provide the same protection to a 'recent occupant' of a vehicle as to a recent occupant of a house."

"Without some limiting principle, I fear that today's decision will contribute to 'a massive broadening of the automobile exception,' when officers have probable cause to arrest an individual but not to search his car."