I have been using the eye-fi card as my primary memory card since the middle of February. The card is still working fine and handles shooting RAW and JPEG during casual photo opportunities. I have not really pushed the limits with fast frames per second. Tomorrow, I am receiving two Compact Flash cards and then I will be primarily using the eye-fi card to save JPEG files while the CF card will save RAW files.
The one thing that I will say is that I would not use this card for RAW files on a regular basis. The reason being that RAW files are large. It takes a long time for them to transfer from the camera to the computer. The other thing that I am noticing is that the software keeps track of which files have been uploaded to the computer. A couple weeks ago I took the card out of the camera and did a direct transfer to my computer which was much faster. However, the software had no record of the file transfer and therefore it went through the process of transferring all of the same files via the wi-fi connection on a later date.
So, my overall conclusion from the experiences with the eye-fi card so far are: use it for JPEG files because they transfer much faster, and let the software do the transfer unless you want two copies of the same file on your computer. Another thing that I have been doing is in the first camera setup menu, there is an option to turn on and off transferring from the eye-fi card. I turn off the transfer while I am out shooting pictures. A) I am just guessing that it saves a little bit of battery power because the card isn’t searching for the network connection, and B) I set the card to be as secure as possible, but I am not sure if it is going to find a stray connection or if the connection is visible to the public. Eventually, my plan is to use the card in connection with an iPad for infield previews of the JPEG files.