I do not buy the argument that gun registration will reduce gun related crime, and here is why.
The argument is that if guns are made harder to get, then at least some criminals who use guns in the course of their "work" will be deterred--perhaps switching to non-violent theft, or even going legit.
I doubt many will argue the war on drugs has been a success. One can count the quantity of drugs seized in the United States, which was 1,626 metric tons between January 2009 and November 2009.
http://www.justice.gov/ndic/pubs38/38661/movement.htmIt is not known what percentage of smuggled illegal drugs make it into the United States--although I will state the obvious and say the number must be between 1% and 99%.
Drugs are a consumable product that feed an addiction. In the course of crime, guns are a durable product used as tools to perpetrate crime. If illegal drugs can make it in, then guns can certainly make it in through illegal channels to be supplied to criminals.
Because guns are not consumed in the course of perpetrating crimes, one gun can be used by one criminal to perpetrate many crimes. Because guns are not consumed, then the markup on guns in the course of importing them is not going to drive up the price of illegal guns such that criminals cannot afford guns to perpetrate violent crime.
The only things registration can lead to are unnecessary expense and bureaucracy at best and confiscation at worst.
One of the unintended consequences of alcohol prohibition was an arms race. If smuggling 50 bottles of gin was just as illegal as smuggling a six pack of beer, and one were going to violate the law, then one may as well increase the profit margin to alter the risk/reward ratio. If most guns to criminals enter the country through illegal sources because of registration, then I suspect a significant portion of the smuggled guns will be honest to goodness fully automatic rifles and sub machineguns--not inexpensive $100 handguns.