Probably quite a bit.
An airline passenger just wants to get on a plane, have a relatively pleasant flight and arrive safely at a destination without being scared to death.
All of us who fly occasionally have thought about the unthinkable: what it would be like to be on a doomed plane. The first indications that something has gone wrong. The precipitous drop as the oxygen masks dangle down and your stomach turns over. The panic in the cabin and the last few seconds of absolute terror before impact.
We've certainly thought more about it since the Sept. 11, 2001, terror attacks.
We can only hope that those aboard the three hijacked planes that plunged into the World Trade Center or the Pentagon were numbed by the unreality of what was happening to them, or alternatively warmed by thoughts of those who love them.
We can also hope that we would have had the courage of those aboard the fourth plane, charging the cockpit and forcing the aircraft into the ground of Pennsylvania. I suspect that not many of us would.
Which brings us to the latest effort by the government to keep terror from striking again.
The Transportation Security Administration has announced a new system for background checks of those attempting to board an airliner, something called the Computer Assisted Passenger Pre-screening System II.
CAPPS II, obviously the successor to an earlier program, would divide prospective passengers into green, yellow and red categories.
Those who register green on an extensive computer background check would go through security rather quickly. If you register yellow -- and there's been no clear indication of what criteria would be used to determine that designation -- you probably would be pulled aside for questioning.
If you registered red, you would not be able to fly. You might even be arrested.
The system will be tested at several airports over the next few weeks. Eventually, it will expand to all airports in the United States.
The American Civil Liberties Union, among others, is sounding a warning.
"CAPPS II is based on the same concept as the Pentagon's 'Total Information Awareness' program, which proposed massive fishing expeditions through some of our most personally sensitive data," said the ACLU's Barry Steinhardt this week.
Steinhardt is the director of the ACLU's Technology and Liberty Program.
The ACLU's legislative counsel, Katie Corrigan, issued an even more pointed warning. "This system threatens to create a permanent blacklisted underclass of Americans who cannot travel freely," she said. "Unfortunately, history suggests that the government will be capricious, unfair and politically biased in deciding who to stamp as suspect. Anyone could get caught up in this system, with no way to get out."
Of particular worry for civil libertarians is that a yellow designation on the airport watch list would be shared with other government agencies at all levels, including the CIA and foreign governments, according to the ACLU.
The acting under secretary of transportation for security, who heads the TSA, is Adm. James M. Loy.
Loy explained in a January speech why the administration believes the system will be more effective than the present "watch list" used at airports.
CAPPS II "is really three-fold in nature," Loy said. "The first goal is to ... take the system that is currently dealt with and managed by the airlines themselves, relieve them of that responsibility and pull the system inside this TSA ... "
The second goal is to strengthen identification of passengers. After passengers buy tickets, they are required to provide photo identification to board a plane.
Under the present system, that photo ID may have been obtained from "from the same guy that sold me the watch in Battery Park yesterday morning," Loy said. In other words, it's too easy to get a fake ID to support a false name. A computer database would match the names and descriptions -- "some kind of law enforcement standard for identification" -- to the massive federal computer database.
The third goal, Loy said, is "to bounce that name that we now have some confidence in off an integrated watch list that truly represents foreign terrorists so that we can make good judgments as to who in that millions of folks coming to the airport on a daily basis deserves greater scrutiny ... before they board the aircraft."
The admiral said he has great hopes that many frequent flyers would voluntarily submit to the more extensive background checks.
The "registered traveler program" would be "be a voluntary program," Loy said, "where people who are willing to put themselves through a more scrutinized background investigation ... will gain 'status,' quote, unquote, with a registered traveler capability, or a number, or a card or whatever we might manifest it as and facilitate the process of what we do in managing flow through our airports much better. Those who are registered travelers will have identified themselves well in advance as folks requiring normal scrutiny rather than heightened scrutiny ... "
Depending on your point of view, Loy's comments should either alarm you or reassure you.
But how will CAPPS II and other administration security programs play if they are challenged in federal court?
My guess is that they would fare pretty well.
The last major decision by the Supreme Court on unreasonable search and seizures came in 2001's Kyllo vs. the United States.
The case involved the use of thermal imaging -- using a heat-sensing device -- to scan the outside of homes in Florence, Ore. The device, operated from the street, discovered a marijuana grow lamp inside one house.
Justice Antonin Scalia, writing for a 6-3 majority, said the use of thermal imagery without a warrant was an unconstitutional violation of the Fourth Amendment.
"As Justice (John) Harlan's oft-quoted (opinion) described it," Scalia said, "a Fourth Amendment search occurs when the government violates a subjective expectation of privacy that society recognizes as reasonable."
The key word is "expectation."
It's a consistent standard used by the federal courts. In many aspects of our lives, we have an expectation of privacy. If government violates that expectation it violates the Constitution.
But when it comes to airline security, we have already traded much of that expectation for a degree of safety. We allow strangers to scan our clothes for metal and rummage through our luggage before we board a plane.
The federal courts might be inclined to believe we are willing to trade a great deal more for the right to fly in safety.
Eventually, historians will have the final word on what effect all of this has on a once totally free society.