I just returned from a lovely vacation in Playa del Carmen, Mexico. The hotel I stayed at had Wifi, and I took my trusty D50, Eye-Fi card, and my Linux laptop. But, I never actually used the card. I stuck with my trusty non-Wifi Sandisk card.
Why? Well, I promised my lovely wife that the laptop would stay in its bag except for checking flights (we were affected by American's MD-80 issues). It's a bit hard to program the new network names into the card without the laptop, so it went unused. I also did not want the card sitting in the camera without using its wireless capabilities because the only time I've ever been concerned with battery life in my SLR has been with the Eye-Fi card in it. Contrary to what is in the FAQ I do seem to feel the battery life shorten significantly with the card in there. I wish I had an A/C adapter and an ammeter for my camera to measure this.
Anyway, I really do wish there was some way to configure the card out in the field, or even shut off the radio. I'd love to not have to lug my laptop around (I really need an iPhone). Perhaps the card could populate the image folders on the card with partial ESSIDs for the open wireless networks that it sees. If I changed the active folder on the camera over to one of those, the card could start using the new network. I bet this would be nearly impossible to get working on all cameras, but it might work on a good subset.
Maybe other features of the card could be enabled or disabled by having the user view and delete pictures on the card. Could the card detect when the camera deletes a picture that had an image of "RADIO OFF" in it and actually turn off the radio?
That's really why I'd love to hack the firmware. I could customize the card for me and my own perverted personal use like I do with my kernel.