I was just checking out Tumblr and I have to say I am really impressed. This is a service that could well take a large chunk of users from blogspot / blogger and wordpress.com. It's probably far more suited to the quick posting and deed / link aggregation that a many people do than traditional blogging tools. They are allowing advertising (at least AdSense for now), has anyone tried monetising / building up a popular blog with Tumblr?