To make things more intense, exciting, or interesting.
(introduced by chef Emeril Lagasse in reference to spicing up his recipies)
Guest: Dude, this party sucks!
Host: Let's kick it up a notch! (brings out strippers and beer)
The epicenter of a disaster or explosion.
Currently, the term is most commonly used in reference to the location of the World Trade Center after the September 11th attacks.
It took much less time than expected to clear the debris from ground zero.