Excessive speed or criminal speed in Arizona is a class 3 misdemeanor carrying a maximum penalty of 30 days in jail and up to a $500 fine. Speeding can become a crime under a couple of circumstances:
If you are found guilty, the MVD (http://www.azdot.gov/mvd/) will also be glad to add 3 points against your license and perhaps send you to defensive driving school. A criminal speeding ticket could also lead to a suspended license and other penalties imposed by MVD.
Therefore, excessive speed should not be taken lightly. It is a crime.