Legally, in most (if not all) of the US you /can/ be cited for tailgating (the laws require a minimum following distance).
Reality is that the traffic cops seldom ever cite for tailgating in general. If one were to see a citation for such, it is likely after an accident where the officer can deduce that the cause was "following too closely" and so they then issue the citation.
In Australia, if you are the rear vehicle in a rear-end accident you are automatically at fault in almost all circumstances. The only exceptions I know of are if the front car pulled out immediately in front of the rear car, or if the front car was reversing.
I think that driving close to the car in front of you is the number 1 cause of accidents. Much more dangerous than driving fast.