Not wanting to go to far off topic to the OPs post, but the green drives have their place. You wouldnt want one as a main drive in a gaming rig, but as a storage drive their fine and in a server environment their essential, even though their slower they do use less power and even a bit less power in a data center means a lot of £'s saved
Not to get too geeky but the WD 'green' drives dont run at 5400rpm they are actually set individually at between 5,400 and 7,200rpm depending on what speed uses the least power for the particular drive

pretty decent for media centre PC's etc or people not bothered about performance.