Tumblr is essentially a blogging platform on which users can easily share other blogs, images, and videos. In fact, like Pinterest, Tumblr lends itself to visual content. As a blogging platform, Tumblr is easier to use than, say, WordPress, and it very effectively allows others to interact with your content. Presence on Tumblr will require a fairly significant commitment to producing an ongoing supply of new content--especially images and video--so it's not for every company. It also tends to attract a younger demographic, which may or may not suit your organization. However, Tumblr is a place where people tend to stop and stay a (long) while, a plus for any business.