Engadget posted a review of the Eye-Fi Secure Digital Wifi card, and summarized it with the following sentence:

Sounds like a great idea in theory, it turns out that the Eye-Fi is, in its current release, an answer seeking a question.

This opinion is based off the fact that you can't use it on any wifi hotspot. The card will only connect to computers that have been pre-configured with software that will enable it to receive the pictures, and only on the same access point as the camera.

What they fail to miss is how useful this card is to anyone who shoots events or works in a studio, and prefers to work without a cord tying them to a machine. By setting the system up to auto-download the images to a computer (even if they are not uploaded to an online service), you can enable some pretty nice workflow options. Adapters for most cameras to enable them to transfer pictures to a computer as they are taken are usually very pricey. Allowing this with any SD capable camera just by purchasing the card is awesome.

I do agree that having the card work on any public wifi hotspot would be cool. I just don't think every product must be usable by any random person to be useful.