bah, all these "terrorist warnings" are just media plays for better ratings. if everybody thinks that they have to watch the 5 o'clock news in order to know how to avoid terrorism, the shows will get better ratings and more cash from adverts and such.

in reality, these "terrorist warnings" are usually nothing more than what your average 12-year-old could come up with just done up a bit to sound more official. i mean they all work on one concept and no spefic threats: "terrorists could go after our infrestructure".

wait, you mean a terrorist could be dastardly enough to attempt to blow up a power plant? PURE GENIOUS!</sarcasm>
please, more like common sence. hell, its what we do in war all the time. take out the infrastructure(power, phone, ect.) and its easy to just roll in and take the place over(or as we like to put it "station a piece keeping force")

edit:
NOTE: i am not implying that terrorists use the same rules as nations do in wars, i'm just showing how hitting the infrastructure is nothing new, and is an obvious move.