Just to keep things in perspective:
US Murder rate 1980 10.2/100m population
US murder rate 2009 5.0/100m population (Most recent year given)
Looks like a pretty steep drop to me. Is this because of or in spite of guns being more common in our society? Because of or in spite of more and more states having concealed carry laws?
US violent crime rate 1980 507/100m
US violent crime rate 2009 429/100m
Table 306 Statistical Abstracthttp://www.census.gov/prod/2011pubs/12statab/law.pdf
Lots of other interesting stats in that chapter on law enforcement and crime if you want to just noodle around a bit.
For those not familiar with the Abstract, it is a pretty fascinating book to just open up at random. As its name implies, it has statistical information on pretty much every aspect of American life going back, in some cases, to the what they call Colonial Times, before the US existed. Also a whole chapter of international comparisons that is pretty nifty.