It's just like the SD memory card that you use in your camera, but any picture you take will wirelessly transmit to your computer instantly, so you don't have to connect your camera to the computer or take out the card to download the pics when you're done.
It features an "Endless Memory" mode where it'll automatically delete pics, starting from the oldest, to make room for new ones. That way you never to have to go through and manually delete pics to make room, and it knows to only delete the pics already safely transmitted to your computer.
One useful application, especially for bloggers, is to have it transmit to a mobile device like a laptop or an iPad that's placed wherever you're taking your pics... then you can see the full-size images right away as you're taking them! I think you can also have it to upload select or all pics to many popular online galleries without needing a computer, which is ideally good for traveling.
their website, and here's their promo video: