I personally like the idea with two exceptions: The previously mentioned steep cost increase, if it really occurs, and the requirement for untagged ammunition to be destroyed by a fixed date. Like ea6bflyer said, they'll catch a lot of dumb criminals, which in my experience is >75% of criminals in gun crimes. Sure, the really determined assholes out there will take it upon themselves to learn to reload rounds, but Jimmy the Crackhead in Detroit isn't going to waste his time with that IMHO. The increased cost and required destruction of rounds only hurts legitimate users though. The people who have large stocks of ammunition in their basement that would have to be destroyed aren't usually the type to go spraying and praying in Toys R' Us. They're usually cheap bastards such as myself who prefer to buy ammo by the case lot rather than be nickel and dimed on every individual box.
All that being said, I think that no matter what happens, the two retardedly polarized sides in the gun debate will make this into enough of an issue that it'll aggravate all of us who legitimately shoot.