Results of power usage study on my desktop spock (i.e. plugging it into a wattmeter and running through things): Difference between S5 and S3, about a watt, maybe less. Difference between S0 idle and S3, about 45 watts! Effect of power-save settings, about 5 watts. Difference between S0 running and S0 idle, 15-25 watts. With the power-save settings on, resuming from S0 idle doesn't work. In conclusion: Use S3 as often as possible.
