I've used the eye-fi card (Mobile X2 8Gb) on a trip down the pacific coast last month. The eye-fi card has worked surprisingly well. I only carried my iPod touch and could transfer pictures and upload to cgoab. I did not need to have wifi available for camera-iPod transfers since my card came with direct mode compatibility. So I could transfer pics anywhere, anytime and prepare my posts via email in my tent. I would generally send my posts in batch as soon as i got wifi.
Here are a few comments:
1. Before buying, check on the eye-fi website that your camera model is supported.
I learned it the hard way when my camera wouldn't initially recognize the card. An eye-fi firmware upgrade fixed the issue.
2. Setup the card correctly on a computer first. Some settings cannot be changed from the iPhone app so make sure everything works fine while you still have access to your computer. For example, I could only activate direct mode from within the software on my MacBook.
3. Be patient. The software interface is pretty clunky so it'll take a few tries to get everything running smoothly. The installation is pretty tedious and reminds me of some pre-2000's software setups. The eye-fi app has a bad rating in the AppStore and that's mostly due to the complicated setup. Once it works though, it works flawlessly.
4. Transfer-wise, it takes about 3-5 seconds to transfer a 5Mb pic from the camera.
5. Distance-wise, i've had it work for up to about 10m, but the closer the faster your transfer.
6. Autonomy-wise, it didn't penalize the camera's battery life to the point where I felt it was unacceptable. I could go for about 10 days on two camera batteries, which sounds reasonable to me. I take a lot of pictures. I think the real consumer was my ipod (with wifi activated) which i usually tried to have plugged-in somewhere during transfers.
7. It is safe to turn-off the camera or receiving device during transfer. It will resume where you left off without corrupting files.
8. Final comment, for ipod/ipad/iphone users. Life is so much easier if you jailbreak your device! All features of the cgoab website work on my jailbroken ipod, including the upload button and maps. You have complete access to the device's filesystem. I still use the email feature because i find it convenient. If you do, on a jailbroken device, you will be able to upload as many pics as you want by email (no 5-pic limitation). You will soon find out that the 5-pic limitation is due to bad memory management of the Mail app. It actually loads all attached pictures in memory while you compose a message. So, say on a 128Mb device, you will probably not be able to upload more than about 7-8 pics without your system locking up. Ipad users wouldn't have that problem.
It was a pretty positive experience so far...and a very light setup.
1 camera + eyefi + ipod touch and its charger was all i needed to keep my journal up2date (both pics and text this time!).