"What makes this combination way cooler than just a normal SD card or a USB cable to a computer is all the infrastructure provided by the Eye-Fi service — not just transferring images to your computer, but pushing them to your smartphone, photo-sharing sites like Flickr, issuing email or Twitter notifications, etc. This is all configured through the Eye-Fi application — there’s no additional coding required."

Indepth here: http://www.ladyada.net/