I bought an
Eye-Fi Pro X2 card for my Canon IXUS whilst on holiday. This is mostly just random notes and experiences I've had with it so far.
There are
multiple models of Eye-Fi cards and they differ on speed of the flash, storage, WiFi geotagging support and hotspot access. Geotagging and hotspot are optional extras for the lower end models. The price difference between the Pro X2 and the various other models of Eye-Fi cards was small enough that I just went with the Pro X2. I don't need the RAW support but its there if I do. *shrug*
The card itself isn't very smart and the designers have admitted that there is very little resources available in the SoC inside the card. The WiFi network must have DHCP running. The computer running the Eye-Fi software must be on the same subnet as the Eye-Fi card for it to be able to do a direct transfer. The card and software rely on a server run by Eye-Fi to work fully. Its possible to make it work without access to this server but it involves some fiddling and features like geotagging won't work.
If you want to use any of the online photo uploader features e.g. upload to Facebook or Flickr or do a transfer if you don't have the software running somewhere locally then all your photos are relayed through the api.eye.fi server which actually does the transfer on your behalf.
The tiny antenna inside the Eye-Fi card and the sub-optimal positioning of SD slots in cameras means you need to have a very good signal for it to work. If you buy one then don't be surprised if you need to be in the same room as the AP.
The Eye-Fi software is a big Adobe AIR app so only Mac + Windows. The geotagging has to be done via WiFi as its part of the transfer process with the Eye-Fi software. The software contacts the Eye-Fi server and supplies the recorded WiFi AP details to hopefully get the coordinates in return.
The possibilities of hacking the Eye-Fi card itself are fairly minimal. It runs eCos and is very locked down. Firmware updates are model specific and tailored specifically for your card + serial number as the hardware is apparently identical between all cards.
People have managed to replicate most of the functionality of the Eye-Fi software though. I've got a
C++ based Eye-Fi software clone running on my Linux server which will accept photos from my camera locally then run a script which geotags the photo using the Skyhook DB and then rotates it for me as necessary. I just grab them via Samba or NFS afterwards.