I think both with continue to co-exist and will also see a trend of centralizing our posting at one place. In fact, we are already seeing it with Posterous and Tumblr. It allows much more freedom to users.
I also think twitter is paving way for mainstream blogging, as it attracted so many mainstream users requiring so low commitment from users to engage and got people into habit of opening-up and sharing more and more of their thoughts. Eventually they will sure long for more freedom and blogging is the answer.