If what is meant by '9/11 style hijacking' is taking over a commercial plane and using it as a missile -- well the threat of that is quite unrealistic today. Not only is such a plan virtually impossible today, it was impossible by the 4th airplane on the morning of Sept 11. Once word got out what the purpose of the hijacking was -- and no one is under any illusions today -- it is clear that a handful of hijackers could at worst blow up an airplane or crash it into a field somewhere. Use it as a bomb to blow up something else -- that is extremely unlikely.

And while an exploded plane is obviously not something to be desired, it is also true that Air Marshals quite useless in defending against this 'threat'. I'm not sure what exactly they are supposed to do about someone who gets a bomb onto a plane in his checked luggage, for instance, gets on the plane and blows himself up along with all the other pax (and air marshals). And as people have pointed out, air marshals are simply a misallocation of resources when it comes to protecting ports, nuclear facilities, chemical plants, etc.

The real purpose of post-Sept 11 security measures, I've always thought, has much more to do with reassuring people -- esp those who don't fly a lot -- that airline travel is safe. As I see it, the whole purpose of these measures is pr, entirely linked to the importance of keeping the airline industry solvent -- and politicians in their jobs -- and, for many of the reasons pointed out in this thread, has almost nothing to do with actually making flying safer.

Of course to blame air marshals for all this is kind of silly.

Just my 2 cents.