A nuclear bomb in several cities would effectively destroy the world economy and essentially send us back to an agrarian society. Technological knowledge would be abundant but useless without the money to re-build and re-design the machines that bring convenience to our lives.
The consequences of such horrific acts are mind boggling. Only God could save us in that event.
Depending on the location. A nuclear bomb, or 3 as claimed for that matter would certainly decimate the immediate vicinity of the city in question, and if that city was a major center of commerce like NY or Boston then yes a significant effect would be seen. Keep in mind though, as horrible as a nuclear attack would be, the weapons would not wipe out civilization as we know it. We could be plunged into a depression, but not unless all major centers were destroyed would we see something along that lines you are suggesting. Although our lives would certainly all change, it would not be the imagined post-apocalyptic image which you convey. The major destruction would be limited to the city (maybe the whole thing, maybe only part depending on the yield).
Furthermore, reading about all this can make you justifiably nervous, but you should not let it make you overly crazed. The fact is that the US has often been overshadowed by the threat of nuclear annhilation. The doomsday clock is set at 7 till midnight, but its been closer in the past. You just have to accept the possibility that an attack IS possible and understand what that means. Facing and coming to grips with something is the first step to conquering fear of it. And lets face it, weither real or imagined, this threat or usage of force is a tool to create terror by them. Do not give them what they want. If it is your day to be called home (i.e. die) then you'll get hit by a bus, blown up or have a heart attack. We are all mortal, and must accept that each day could be the last one. I do not mean to sound defeatist...on the contrary...I make the point that only when you confront that fear will you be able to function without it. And with that comes the knowledge and power. To fear death is to be crippled by it. If the worst thing that could happen is death, than you are better off than some others out there.
-wow that was a dark post, but alot of people on the thread, myself included, find its easy to let this worry run away with them and wonder weither an attack will happen today. I want us to stop an attack, but there is realization that in this is a no-rules fight and we may not be there at the end of it. Be steadfast, and hold the line.