Most, but not all, of these sites were created with Tumblr, a dead-simple two-year-old blogging tool that has swung open the publishing industry for anyone with a gift for snark and lots of extra hours to kill. The term tumblelog—a blog that points to cool stuff elsewhere online—actually preceded the invention of Tumblr, but the software offers a few features that make creating such pages supereasy. Tumblr includes several stylish themes that obviate the need for designing anything yourself, and it comes prepackaged with templates for different kinds of posts—it makes your photos look different from your videos, which in turn look different from quotes you pull from other sites, etc. In other words, Tumblr lets you create a great-looking blog in two minutes flat.
This is Why You're Fat: The Allure of Single Topic Blogs -- Slate.com
Love Tumblr. My absolute favorite way to blog these days. It's like a perfect little internet scrapbook.