According to the usually very erudite usability specialist, Jakob Nielsen, yes, blogging is a waste of time!
However, although I do find Jakob Nielsen’s article very interesting with several valid points, I think he misses out on certain central points.
1) Blog postings can be high quality and used to sample ideas/get feedback.
According to Nielsen, our time would be much better spent on writing fewer well-reflected articles in subject areas where we have knowledge. Although I appreciate this point, I still think the blog may serve as a sandpit for ideas, possible even first drafts for some ideas that later make it into an article. Also articles are often longer under way and in terms of online media thing may have changed dramatically during this space of time.
2) Interaction is the message.
Although Nielsen in his profession, may be better off by writing regular articles on his areas of expertise, I would argue that especially politicians (as discussed in Nielsen’s examples) might benefit from a dialogue and asking for user participation. I am by no means advocating that user dialogue is the only form of communication, but I think the user participation is ever more important.