Some numbers about power consumption of hard drives….
Maxtor DiamondMax 10 6L300R0, 7200 RPM, 300 gig (279.48GB formatted) ATA hard drive has the following power consumption: +5V 740 mA, +12V 1500 mA.
Seagate Barracuda ST3300831A, 7200 RPM, 300 gig (279.45GB formatted) ATA hard drive has the following power consumption: +5V 460 mA, +12V 560 mA.
Observations: Seagate has a 5 year warranty on their drives. Lower power consumption means lower power dissipation, and thus cooler system. Lower power consumption means that you can get away with smaller power supply (or more drives in a system), and thus reduce your power consumption costs (that are more of an issue in a 24/7 environment) and air conditioning/cooling costs.
Conclusions: One should spec hard drives not only from the point of view of costs (WD is cheap but in my experience dies like a butterfly under a cold spell), but from the point of view of warranty and power consumption. Sadly vendors do not provide power consumtion information in their spec sheets, so the only way to find it out is by going to a computer store, asking to look at an OEM drive, and reading off the numbers.