I have the Kodak W1020 10" WiFi frame. It does have a unique serial number which is available on the web interface. When I signed up for FrameChannel, I had to provide a 4-digit ID displayed by the frame (don't remember now what it was, or whether it was related to the serial number or the MAC address, and it can't be displayed again without re-initializing the frame). To connect to my Kodak Gallery online account, I had to provide the frame with my email address and password. To sign in to FrameChannel on the web, I have to provide a username and password. In the My FrameChannel Advanced Settings there is a 4-digit PIN number (purpose undocumented).
So, in summary, every bit of capability needed for security is there, awaiting a quick firmware update. It was just a bit of carelessness that FrameChannel didn't think hard enough about security in the first place. I'm willing to forgive this as long as they get together with Kodak quickly and issue a security update - it's a pretty new service, and they are still evolving rapidly. I certainly would never put any private/confidential photos on a web server of any kind. Anyone that does is naive to think it's secure. But I don't want morons defacing my frame contents.