The Postagram Postcard app (Free—iPhone/Android) is a really neat idea. It takes images from your Instagram service and transforms it into and sends a postcard at $.99 each. The Instagram picture you use will pop-out and be a stand-alone picture if you don't want to keep the entire card. All you need is the recipient's name and address (stored after they're entered once) and a credit card (also stored after entered once). You can also send a personalized 140-character message (like a tweet). After that in 2-5 business day (and slightly longer for overseas cards) the recipient should receive the card in the mail.
Sounds reasonable and pretty easy, right? Well, with everything new and novel there always seems to be a price and with Postagram there are a few.
First, with this service would it be difficult for a stalker or predator to hunt down your address on the internet? After you create your account with Sincerely (the developers) you can build your own personal address book. You can enter the information your have for friends and family, or, you can email a message to people (can be anonymous, by the way) asking recipients to enter their mailing address in the secure form and send it.
Secondly, the cloud servers where Postagram Postcards are stored is not secure (not signing or using Cloud-front features) and their naming conventions are predictable. This means everything is easily hacked and viewed and your images are not private.