Tough to tell how common this is, the NYT makes it appear these sheriffs are a bunch of hicks restricted to Colorado and upstate NY, but I suspect it's a phenomenon more widespread than fully reported -
"The resistance of sheriffs in Colorado is playing out in other states, raising questions about whether tougher rules passed since Newtown will have a muted effect in parts of the American heartland, where gun ownership is common and grass-roots opposition to tighter restrictions is high."
http://www.nytimes.com/2013/12/16/us...trol.html?_r=0
State legislatures push unworkable laws and the sheriffs say screw it, we aren't enforcing stupid laws. And why not? You could say they're just taking a page from the Obama playbook. They didn't like DOMA and they refused to enforce it. They don't like big chunks of the ACA, and suspend enforcement of several of the statutory deadlines in ObamaCare that Congress passed under the direction of the Obama administration.
IMO the Obama administration has created such a disrespect for Washington and the rule of law we might be sailing into another Nullification Crisis. Then life will really get interesting