I picked one up to use with my LX3 about a month ago and have been having fun with it, but agree with what gostwyck is saying (though I found the transfer speed to be about 30 seconds for an 11MB file). It is much slower than shooting tethered via cable and I wouldn't suggest using Eye-Fi as a replacement if you can shoot that way, but I think it has some good uses when that isn't an option.
Here's a rather
novel use.
I believe the geotagging is based on where your Internet connection is as opposed to where you were shooting at a given moment, but I could be wrong about that as I haven't looked into that part too deeply.
You can also set it up to also directly upload to various online photo sharing sites (flickr, facebook, smugmug, etc.), which might have appeal to some folks.
For me, I was more curious about finding solutions for shooting tethered for cameras that don't otherwise have a tethering option (such as my LX3), and while the 30 second wait was a bit of a drag, it was easier than popping the card after every shot to copy it to my computer and import it into Lightroom. Instead with Eye-Fi I was able to set it up to save to a folder watched by Lightroom and have it automatically import while I was shooting. I could not ever do that before with that camera.
I have been having fun with it though. I took my LX3 out just shooting for fun, along with my Verizon Mifi, and was automatically uploading to Flickr while I was out. Could be useful on trips for sharing with friends/family. When I came home I just set the camera next to the computer and went off to do other things. Came back and all the shots had been automatically imported into Lightroom.
So, I think it is novel. I think it has potential to solve some problems for some folks. Was that worth the $129 I paid? Not really to be honest. I mean, I certainly don't need to shoot tethered with the LX3 when I can do it with my DSLR instead.
It does suck the life out of your camera battery much faster.
It is much slower than you'd want in a studio setting.
The $129 model is currently the only one that will transfer raw files (I think), so you'd have to decide if all that novelty was worth the price for you.
Now, if that transfer speed ever drops under 10 seconds it might be a whole lot more useful.
