I recently bought a completely new PC, because my water-cooling leaked and I was fed up with it and wanted to start from scratch. The new system has top-notch components that deliver extremely fast performance in games, video-encoding, etc. I "accidentally" bought two 1TB Western Digital "Caviar Green" (product-code WD10EADS).
These disks are more than mysterious. Nobody seems to know how many rpm they spin at. Some resellers list them with 7.200rpm, others with 5.400rpm. There are even specifications stating "5.400-7.200rpm", which could be an indicator that they are "Green", because they spin down when not heavily used. Seems like a nice technology - get all the performance when needed, keep noise and power consumption low when not. It's the first time I've heard about this and it's still only an assumption. Western Digital states disk-speeds for their blue- and black-series with 7.200rpm, but the green-series is just missing the specs.
My actual experience with these disks is... frankly put, horrible. I created a RAID1 of two of these disks and made one 100GB partition for my Windows 7 installation and the rest for game-installations, movies and all the other stuff. Windows-installation was quite smooth (if that's even possible), but system startup and program startup times were disastrous. When the system booted with nothing but Firefox installed, while it was still doing it's usual post-login stuff, starting Firefox took something around 3 minutes. This, of course, does not apply when the system startup was completed and the disk was idle. My impression is that overall data throughput is quite ok with these disks, but seeking and concurrent accesses totally kills performance. I'm sorry I did no benchmarks with actual values I could present, but my subjective impression was more than enough for me to decide that I'll return these disks. I think I'll choose the Western Digital Black series instead (which has double the power consumption according to the manufacturer).
Don't get me wrong - I don't think these disks are bad overall. They are just put to use in the wrong place. I can see good usage for them in external usb-housings or as a second data-drive in an office computer. Or an internal or external backup medium. But not as a system drive or a drive that is accessed frequently and concurrently. What I am most angry about is Western Digital's information policy. Why can't they clearly state how the disks work and how much rpm they spin at at what conditions? Holding back information about your products is nothing I can accept.