You're right. Twitter, Flickr, blogging and all that good stuff is completely peripheral to my work. But if you consider the whole of my work-life, it's become essential.
Case in point: my mom checks my twitter. And my -- now dispersed -- extended family posts pictures to a family photo blog to stay in touch. And more than one business opportunity has come to me through friends that I've made through the blog.
Good conversation here, some really rich comments.