latest Mac Mini Server ($999 with the server software, 2.53GHz, Core 2 Duo, 4GB RAM, 1TB disk, but no optical) draws 14W at idle according to apple it even lower processor's speed between keystrokes...
Efficient power supply.
Mac mini includes a highly efficient power supply that reduces the amount of power wasted when bringing electricity from the wall to your computer. Lower power consumption reduces energy bills and lessens the environmental impact of greenhouse gas emissions from power plants.
Advanced power management.
Unlike a lot of Windows-based PC systems, Mac mini uses energy-efficient hardware components that work hand in hand with the operating system to conserve power. Mac OS X spins down hard drives and activates sleep mode. And it balances tasks across both central processors and graphics processors. Mac OS X never misses a power-saving opportunity, no matter how small. It even regulates the processor between keystrokes, reducing power between the letters you type. That’s just one of many ways Apple manages small amounts of power that add up to big savings.
Mac mini is a great example of Apple’s energy-efficient design philosophy. It uses less than 14 watts of power when idle — that’s something no other desktop computer can do.