Perhaps it's not actually meant to be an over the counter, retail item at all.

Could it be aimed at consumer electronics applications like PVRs, music servers, or even games consoles? If given big enough numbers WD can shave a couple of percent off the cost of these beasties by not squeezing them into a slightly smaller box then I can't see that a non-standard form factor is going to worry the likes of Sony et-al and they may even see not letting the user swap in a commodity replacement when the original fails (or a capacity upgrade is needed) as an advantage...

Chocolate Teanot

It's standard enterprise drive size, like the VelociRaptor 300Gb (also 15mm), but instead of speed, it's built for capacity, you could use it to replace a tape backup solution (low power, high capacity, faster than tape), for the price, failed drives can be considered "consumable", at the moment we do disk to disk backups, and then backup the copy to tape (minimal downtime, or zero downtime minimal I/O impact), but the disk is expensive, this is "a" solution.

I suspect (as a previous poster said), this is obviously not designed for laptops, there are many other appliances such as PVRs (I have CCTV recorder and audio jukebox that this would fit in), and of course, you could fit it in a 3.5" bay with an adaptor, combined with it's low power and better airflow it would be much cooler too, I wonder if they would fit in iMacs?

Don't forget that WD are also building the ultra slim 7mm drives too, this isn't a killer product, it's a very specific one, just one for a complete range of products.