There was no standard way (june/09) to report on CPU information for i7 within Linux, so i coded a small program that has capabilities of reporting on the stock and overclocked i7. This tool will work only on linux (i tested 64-bit but 32-bit should would too) and on an i7 (tested it on 920). Readme, and Code provided in attachment.
It knows about Turbo mode, Multipliers, Number of CPUs and more (including correct frequency and C-states, especially the C-states). I don't know of a utility that directly gives details of what C-state the cpu ran(in the past some times). Edit: Turbostat in pmtools also gives this information.
POWER Saving If you want to save power, enable C6 state in bios. I did some experiments with how much saving of power C6 vs. only having C0-C1 will give. My readings are as follows, for my idle system the power readout when enabling only C0-C1 states is 206 Watts and the same environment when using C6 state was 183 Watts. Thus, one can save upto 23 watts at idle by just putting your CPU in a C6 states. Note: these results were done on an i7 920 with lots and lots of fans (all set to a specific value), HDDs and other components were made sure to always run within limits and averaged over multiple runs, thus explaining the high idle wattage (one more reason is my PSU is usually most efficient at 85% around >150 Watts). Also, over multiple runs, these values don't budge a bit, in case if you are wondering
Yet another results i obtained was the fact that USB devices are bad for power saving features. Install powertop (should be in the repositories) and note down what devices are causing most of the interrupts. Note, some devices like Wattsup-pro that use usb have a tendency to make CPU always run in C0-C1 state even if C6 is enabled, so be wary if you are concerned about saving power when using these devices. Avg. loss due to these devices is in the vicinity of 8 Watts.
Install i7z-gui on ubuntu
Open the terminal and run the following command
sudo apt-get install i7z-gui