Paul Randal recently blogged about the importance of checking to make sure you are getting every bit of speed you should from your cpus. He recommended that people use CPU-Z, a free tool I recommend and have been using for many years.
Power saving features in a cpu are great for laptops. Battery life is greatly extended when a processor isn't running to the max all of the time. But this isn't necessarily a good thing for a server. As Paul and others have pointed out, the processor might not get back to full speed as quickly as you'd like. For SQL Server, you should consider disabling the power saving feature. Keep in mind that this could make the processor run hotter, which I address in my final paragraph.
My point is to alert you to another problem with power saving features, not rehash what Paul, Brent Ozar, and Glenn Berry have already published. What if your SQL Server is in a virtual machine? If so, do you know what the physical machine's cpu power settings are? Confirming that will require access to the physical machine, not the virtual machine. I have no interest in starting a contentious debate about green data centers, but I do think some of you will find that you don't want cpu power saving features enabled on your physical server.
For those of you who run Virtual PC on a laptop or desktop, you will get better results with cpu power saving features disabled as this KB article explains.
What's nice about CPU-Z and its companion the Hardware Monitor is that you don't have to install them. Just run the exe. Your clients probably don't want you installing things on their servers. With these highly useful free tools, you don't have to install anything. Just run them and use them because they are portable applications.
Finally, when you disable cpu power saving features, you should run the free Hardware Monitor afterwards. Once your cpu is configured to run at the maximum clock speed all of the time, it might be hotter, even too hot. Just last week, after running CPU-Z, I ran Hardware Monitor and discovered an excessively hot processor. Running at full speed made it dangerously hot. The remedy was to remove the fan and heatsink assembly, clean the processor, replace the old silver based thermal paste with a new, nonconductive thermal paste (see review), and reseat the fan and heatsink. Temperatures dropped by over 35 degrees Celsius. If you are responsible for a server and change the configuration to make a processor work harder, you need to be accountable for your actions and confirm that the extra work isn't generating excessive heat.