I've been using CnQ on an overclocked system for over a year now with no issues. By using a third party app (RMclock) to control the throttling and voltages you can eliminate most of the problems, the one main restriction that remains is using the max/default multi for overclocking.
It really works well and gives you the best of both worlds IMO. 95% of the time my system runs just slightly under stock mhz with the minimum voltage that my mobo can supply, which means it runs extremely cool and uses less energy. But when I launch an app that pushes the CPU usage it ramps up (in milliseconds) to my max overclock and voltage settings and stays there until CPU usage tails off then it throttle back down.
Steps to make it work
1. download and install the CnQ driver from AMD's website
2. enable CnQ in bios
3. Download,install and setup RMclock. Or set your power management settings in windows. IMO RMclock gives you much more control over when and how it throttles