I'll just point over to Jeff's blog post on the topic. This is a neat development. It should allow people to do things like keep their pictures private and not upload them at all to the Eye-Fi servers.
This kind of thing could also make a really neat iPhone or Android app, now that Jeff has a proven algorithm. If you can get your phone and your Eye-Fi card on the same WiFi network, you could view things as they come out of your camera.
Anybody know of any tiny battery-powered 802.11 access points? I bet one of these plus one of these would be interesting. I'll have to test Jeff's program with an isolated wireless network and see what happens.