I imagine that people in America can expect this kind of thing all this year.   Timed rightly, public warnings could be a very effectuive electoral ploy for Bush and Co.

At the same time, as has been pointed out, leaking phony threats is a great way for Al Qaida (or whoever) to hit the US economy without needing to do anything partucular.

Either way, spasmodically crying wolf every now and again will just help ensure that the security precautions get increasingly slack over a period of time.

The only sensible way to deal with a continuing threat is to maintain a continuing automatic level of caution, and get used to any inconvenience incurred as a way of life.

For example reorganise so as to cut down on the plane travel (we've got the Internet and all that now, electronic conferences and so forth), and build in the delays at the airports for those whose jourtneys are really necessary. And at the same time accept that you are never wholly safe in this life, and live with that.