I would say that as a regular user of twitter, digg, facebook, etc. that they are just another medium to give access to/promote the blog. What I do think twitter may have changed is the comment/interaction aspect. Someone twitters a link to their blog post. People click it, read the post and then respond via twitter, rather than leaving a comment on the blog. This however creates more discussion as those following that person via twitter, then click on the link as they are curious what the discussion is about. So, no I don't think the blog is dead.