Poking around I've found some interesting info. Wiki says it's all inconclusive at this point.
But consider this (from wiki):
(snip) University of Washington public health professor Brandon Centerwall prepared a study comparing homicide rates between Canada and the U.S., as the two countries are very similar, yet have different handgun ownership rates. He reported "Major differences in the prevalence of handguns have not resulted in differing total criminal homicide rates in Canadian provinces and adjoining US states."[45] In his conclusions he published the following admonition:
"If you are surprised by my findings, so are we. We did not begin this research with any intent to "exonerate" handguns, but there it is – a negative finding, to be sure, but a negative finding is nevertheless a positive contribution. It directs us where NOT to aim public health resources."[45]
Don Kates has observed:
"Scholars engaged in serious criminological research into "gun control" have found themselves forced, often very reluctantly, into four largely negative propositions. First, there is no persuasive evidence that gun ownership causes ordinary, responsible, law abiding adults to murder or engage in any other criminal behavior—though guns can facilitate crime by those who were independently inclined toward it. Second, the value of firearms in defending victims has been greatly underestimated. Third, gun controls are innately very difficult to enforce.
[...]
"Therefore, the fourth conclusion criminological research and analysis forces on scholars is that while controls carefully targeted only at the criminal and irresponsible have a place in crime-reduction strategy, the capacity of any type of gun law to reduce dangerous behavior can never be more than marginal."[46]
(endsnip)
http://en.wikipedia.org/wiki/Conceal..._laws_on_crime
Pete