I think the two are inextricably linked. You can't blog without having an audience which means that you need to have a network. Rarely do you see well known bloggers who don't visit other blogs. Most visit other blogs to socialise, get material, comment etc. In this respect, as I think Gina rightly pointed out the first time, blogs are social networks.
However, to search for new blogs, authors and material in your niche one of the greatest ways of finding new people who share your ideas and opinions is social networking. Sites like MyBlogLog and Blogcatalog are a valuable source of finding new blogs to read. Sites like LinkedIn (and of course SalesPractice) are great resources for finding people and sharing ideas, the people you find there may have a blog or may read yours.
Though I think it is possible to do one or the other (and be successful) the two types of media are closely related and complimetary. I value them equally.
