Reason Engaged: The Council of Tyrant Mayors Concludes:

The representatives elected by the people don't know what's best for them, so their group of activist governors must take it upon themselves to advance their agenda outside the bounds of the working legislative process.
Mayors from 15 major U.S. cities attending a gun control summit called the federal government "complicit' in illegal gun-related crimes and urged it to do more to get the weapons off the street Wednesday. [...] Bloomberg, who has made gun control a priority early in his second term, admitted that the mayors have little power to enact the measures he is promoting, but said the group would lobby legislators and use litigation to create reform.
Crimes committed with guns are worse than the same crime committed without guns. They'll let you off easy as long as you don't have a gun.
The mayors pledged to punish criminals caught with illegal guns to the full extent of the law,
Dealers should be psychic and know who not to sell guns to. The hoops they already have to jump through to sell a gun aren't enough.
[The mayors pledged to] find and prosecute gun dealers who knowingly sell guns to unqualified buyers,
The government ought to spend your money developing technology that doesn't work in order to make criminals out of law-abiding citizens. [The mayors pledged to] develop new technologies to trace guns

Those sound like reasonable and constitutionally defensible measures to me!

Update: Looks like just about everybody is talking about this:

Reason Engaged