Twitter has taken the form of micro-blogging, and can be useful to the non-bloggers out there. Usually I have to first resolve dilemma to whether blog or twitter creating a sense of overlap. But the ones who do not already have a blog, or the ones who have found it too tedious to continue can use twitter to replace it. In fact it can be quite efficient for some to twitter rather than blog.
As Steve Rubel says, twitter can be addictive and complies with the need for continuous partial attention. It can also make someone replace the blog with twitter. However, the essence of it is still blogging – to communicate to others and have a conversation. This is what I think, blogging is polymorphous. I think the services, the types or the trends can keep changing. I am sure there will be more possibilities and more ways of doing it, influenced by technology or influenced by popular preferences but the essence remains. Blogging will continue, because it reaches across boundaries, eliminates restrictions and lowers inhibitions. However be prepared to see it in many more forms.