People don’t like being told what to do. We like to explore, change things around, and make a place our own. Hefty design challenges await the makers of websites where people feel free to engage; both with the system itself and with each other. Embrace the idea that people will warp and stretch your site in ways you can’t predict—they’ll surprise you with their creativity and make something wonderful with what you provide.
— A List Apart: Articles: Community: From Little Things, Big Things Grow. The quote is about Flickr, but it also makes me think of Tumblr when I read it.