Sure, you can already add storage to your Raspberry Pi, but it's usually an exercise in trade-offs: SD cards don't hold much data, and USB drives (even the portable ones) tend to be too big and power-hungry for a mini PC. WD doesn't think you should have to compromise, though. It's shipping a new PiDrive that stuffs 314GB into a slim design that won't overwhelm the Pi's power system, but is fast enough to make full use of the USB connection. It even has a special version of BerryBoot (a multi-operating system tool) to help you load your platform of choice and fill that abundant space with apps.
The PiDrive is relatively expensive. Its normal $45.81 (£39.50) price is higher than that of the Raspberry Pi itself, and even a "limited-time" cut to $31.42 (£27.09) may have you thinking carefully before pulling the trigger. If you have a media server or another Raspberry Pi project that simply can't get by on a few dozen gigs, though, it might be worth shelling out a little extra.