Tumblr is a web 2.0 micro-blogging platform that allows users to post text, images, video, links, quotes, and audio to their tumblelog, a short-form blog. Users can “follow” other users and see their posts together on their dashboard.
Compared to other web 2.0 social internet services:
Compared to WordPress: Tumblr excells at creating little visual interesting posts fast, WordPress is better for the longer more pensive posts.
So you can expect me to spend less time on FaceBook, Flickr, Del.icio.us to spend more time at my Tumblr.