Instattoo is geared for people who don't draw. It works a little bit like a kaleidoscope. Pick a pattern, style, and size, and rotate the design around until you find something you like. The sheer number of variations means you're not likely to end up with the same tattoo as another Instattoo user.
The $4.99 app's interface is pretty slick. You can save designs, share them, and print out high-res versions to hand to your tattoo artist.
The app primarily generates tribal-style tattoos. You're out of luck if you want a Grateful Dead bear riding a My Little Pony unicorn while jumping over a dolphin in a sea of rainbows.
While it may seem a little unusual to have your iPhone design your permanent body art for you, it's probably better than picking an image off the wall of a tattoo shop that 5,000 other people already have inked on their ankles.
I'm not about to take the same plunge as Toyo (see him getting inked below) and get an Instattoo. Most of my ink is railroad-related and I didn't see a "Streamliner-era Burlington Route" option on the menu.
The Instattoo user group may not grow to be as massive as Instagram, but there could soon be a small herd of iOS geeks sporting app-generated tattoos.