"iTat" is a questionable name for a product, but the actual effect of these "iPhone tattoos" looks pretty good. iTat is a system for etching on the back glass panel of the iPhone, which, on the black iPhone, looks like a sort of tattoo. The whole process is being offered by a company called Sirtified, and you can choose a patterned look, etch a picture, or put text on the back of your iPhone in any way you want. Personally I just like the patterns, but I also think subtler is better.
Unfortunately, it's a DIY process. You put a special vinyl sticker on the back of the iPhone, rub in some "Super Magical Etching Fluid" (likely some mix of hydrofluoric acid, not to be played with), then wait a few minutes while the glass gets eaten away. It only takes a few minutes and sounds pretty easy if you follow directions (in fact, you can buy the fluid in art stores, and try etching even without their kit if you want), but the only assurance your iPhone gets is that it's apparently easy to replace the back cover if you need to.
(It actually is very easy to swap the iPhone's back out, though you will need a "pentalobe" screwdriver. In fact, if you're going to be customizing your iPhone with strong chemicals, it's a good idea to remove the backside plate first anyway. --Ed)
Still, if you want a nice etched pattern on the back of your favorite device, no pain, no gain, right? If you do jump on something like this, be sure to let us know how it works out.