On the face of it, an eye-fi card sounds ideal - seamlessly upload images to Flickr and Picasa while walking around town. The reality is painfully different.
On a whim, when one of the office supply shops was closing, I went in and purchased their very last Eye-Fi card and slipped it into my car video camera (I have a DV camera on my dashboard to record idiots doing stupid things). When parked for the night, the car is well within range of my wifi. The card could not upload a thing as its wifi was too poor.
As the card is only produced as Secure Digital instead of Compact Flash, I had to obtain a converter to use it in my camera. It didn't seem to get on too well with my camera or was it the converter and thus was unusable.
Out of curiosity I dug out one of my infrequently used surveillance cameras which takes an SD card and tried it in that. No go - that didn't seem to get on too well either. I moved my car camera indoors to within 10 feet of my router and it picked up my router then began to transfer with painful slowness, one of the videos. A VGA video that took 2 minutes to record would take 10 minutes to upload. That wasn't too promising.
In the end I put the card on ebay and sold it for pretty close to what I paid for it in the closing sale and enclosed the warranty information too. The buyer seemed happy enough. I'm glad I'm shot of it.
This brings me onto those SD to CF converters. They don't actually seem to be that reliable. I had to have two before I got one that only kinda-sorta worked.
Standardisation seems to have gone right out of the window - a different charger needed for every battery. Every camera takes a different battery - each model from each manufacturer takes a weird new battery - just like mobile phones.
There's a lot in this new electronic age that just doesn't quite work. Eye-Fi is one of those things.