I'm not so knowledgeable about this myself. This is what I found....
Here's the description from Amazon:
Pogoplug POGO-B01 is a multimedia sharing device that lets you connect any external hard drive and then access and share your content over the internet. Installation takes less than 60 seconds and there are no monthly fees. The Pogoplug can be configured in a matter of minutes. The web-based setup program detects the device on your network, and allows you to create a username and password so that you can securely access your files from any web browser, anywhere. Mobile access is also available via the iPhone, iPod touch, Android, Palm, and Blackberry. Photos, videos, and music can be viewed with ease -- the Pogoplug will automatically find them on connected hard drives. You can also browse the drives manually, allowing you to download any stored file, regardless of its type. There are no hidden fees with the Pogoplug for remote access -- the account is completely free, ensuring that your only cost for the device is the cost of the device itself. Optional software is available for your Mac, Windows, or Linux computer. It provides desktop access to drives connected to the Pogoplug, and can also copy files to files stored on your Pogoplug drive automatically. Simply configure "watched" folders -- any files added to those folders will automatically be copied to a connected drive on the Pogoplug, ensuring that your latest downloads are available remotely.
There is also a ton of info on these previous SD threads: