First make sure, through the Eye-Fi Center, that Relayed Transfers are disabled and that the card is configured to send photos to your "computer" (once you've run the following guide, the "computer" that the card will be sending to, will be the iPad/iPhone/iPod Touch).
In ShutterSnitch, go to the collection overview and tap the Options button in the top left corner. Choose "Set up Eye-Fi access".
Note that you need to be connected to the Internet the first time you run this guide!
To retrieve a list of your Eye-Fi cards, you need to log into your Eye-Fi account. Type in your credentials and tap the "Sign on" button in the top right corner.
These will be saved securely in the device keychain and are only used for this authentication.
If everything goes well, you should see a list of your cards. Turn on the cards you want to receive images from. This will tell the Eye-Fi server that your device is now the main receiver. The Eye-Fi Helper will automatically find out about this after a little while - but I suggest you close it until you've got transfers working from the card to your iDevice.
Tip: If you have more than one Eye-Fi Card, you can customize the card names from the Eye-Fi Center.
Once you're set up, you can open or create a new collection, take a picture and it should arrive. It can take a little while for the card to discover the iPad the first time it sends an image, so please give it a little time.
..but wait a minute - what if you're on the road, without any Internet connection and you want to switch between two Eye-Fi cards? Well, as long as you've run this guide once, while being connected to the Internet, the devices have been cached and you'll still be able to switch around.