It's amazing when it actually works correctly. It's honestly a hit or miss. Sometimes it'll connect seamlessly other times it won't do anything and an error would appear. It really does come in handy though especially when you don't want to pull out your laptop to sync photos.
I DID love the Eye Fi cards for our travel photos - they were so easy to upload through the Eye Fi app, which was great for backing up our photos while still on holidays. But since Mobi bought them out, the app doesn't pair with our old cards, so we have to resort to using a card reader.