The basic idea behind Pinterest — which lets you create and share collections of stuff you like in any category you choose — has been tried before by start-ups that didn't make much of a mark. This time it might take off. Pinterest makes the process painless by offering a Pin It button that lets you grab pictures of your favorite things as you browse the Web. The site then collects the images on "boards" that other users can follow and comment on. Perusing other folks' boards, featuring everything from picturesque travel scenes to oddly beautiful bacteria, is as enjoyable as building your own. Pinterest is still in private testing, but if you request an invite, you should be able to get right in.