Usually for measuring power usage there are standard industrial power meters used. But anyway, if you want to have your own monitoring of separate appliances with more features then this project might be suitable. AVR based power logger simply logs data to SD card that can be processed and graphed on PC.
As power data is sampled with 9615Hz frequency, it is capable to calculate P=V*I of higher frequency, and waveform voltage patterns. Current value is captured with old TV flyback transformer and 0.2Ohm current sense resistor. Voltage is divided by 2000 and then fed to to instrumentation amp. So it seems pretty simple and easy to build, just be safe when working with mains.