Summary:Eys-Fi makes a nice little SD card with built-in wifi called an Eye-Fi Connect X2 among others. This little gem is great! The title should really be, "Amazing geek toy and CYA device"...
I find the Eye-Fi Connect X2 card and Android Eye-Fi App to be very useful and mostly reliable on my Samsung Galaxy Tab Plus GT-P6210 running both the original Android 3.2 Honeycomb and recently updated Ice Cream Sandwich. There is a great deal of comfort knowing I have an immediate backup copy of every picture I take.
Since pictures are of major importance to me. Safeguarding my photos with multiple copies is a priority. Under normal circumstance, I would take some random number of pictures, head to my laptop or home system, copy the pictures, rotate out the SD card, take more pictures, etc.
I had an original Eye-Fi card from a couple of years ago. I tried a couple of the Linux options like the python powered eyefiserver with some luck. Sadly, at the time, this option was not very portable since it needed an access point plus laptop or similar. Besides, reading the original eye-fi card was a pain for me under Linux.
Skip ahead a couple of years and the X2 versions... and add a tablet or smart phone and Ad-hoc network support of wireless uploads... welcome to a whole new world.
Now with my Android powered phone or my great little Samsung Galaxy Tab Plus GT-P6210 and the Android Eye-Fi App (or IOS App), I just start the App, shoot a pic and have an original sized copy on my phone or tablet!
OK there's a bit more to process of course. Some will not like the *requirement* to have an Eye-Fi account to use the app. Others will note that I needed to register the SD card with a Windows system. I wish that was different, but it's not.
Just as a side note, the Ad-hoc network range was about 40-45 feet as a general rule for quick transfers. As the distance got just past this range, the time to upload increased by minute(s). So, proximity does matter as you would expect for such a tiny device. Also, I did have a couple of times that the Ad-hoc network would not connect. Restarting the app seemed to provide relief.