Legislation has been introduced in 18 states requiring that all ammo sold be imprinted with tracking numbers, and that these numbers (and your identification) enter a state database when you buy it.
In Arizona, the legislation introduced into the house as HB 2833 and states that "beginning January 1, 2009, a manufacturer shall code all handgun and assault weapon ammunition that is manufactured or sold in this state" and that "beginning Janualry 1. 2011, a private citizen or a retail vendor shall dispose of all noncoded ammunition...".
So all that ammo people are stocking up on now will be illegal in 2011. That's 4 years from now.
To find out more about legislation in your state or a state near you, visit these folks. They are the ones pushing it on us: