I’ve long been a fan of behavioral profiling, as opposed to racial profiling. The U.S. has been testing such a program. While there are legitimate fears that this could end up being racial profiling in disguise, I think this kind of thing is the right idea. (Although I am less impressed with this kind of thing.)
EDITED TO ADD (8/18): Funny cartoon on profiling.
There’s a moral here. Profiling is something we all do, and we do it because—for the most part—it works. But when you’re dealing with an intelligent adversary, as opposed to the cat, you invite that adversary to deliberately try to subvert your profiling system. The effectiveness of any profiling system is directly related to how likely it will be subverted.