I run an Uno/328 on 3.3V at 16MHz everyday without any troubles.
Yes but you are over clocking the device. The manufacturers do not guarantee that all the chips the make will run under such conditions, or all chips that do run will continue to do so as the components age.
Deviating from the makers specifications is like the concept of becoming an outlaw, no longer subject to an obligation to obey but also no longer subject to it's protection.