It's tough to describe why it is so addicting.
Here is what they have to say for themselves: Think of Pinterest as a virtual pinboard — a place where you can create collections of things you love and "follow" collections created by people with great taste.
People use Pinterest to collect and share all sorts of things -- wedding inspiration, favorite T-shirts, DJ equipment. (I created boards for homes, travel, recipes, books, quotes, and just plain cuteness.) You name it, people are pinning it.
When you start pinning, come find me.
Oh, one more thing, I'm kind of obsessed with these little gems, out in June: