(parts 1 and 2)
Question #3: Talk about about blogging as a sociological phenomenon.
Everyone talks about blogging like the first phenomenon to be explained is why people have blogs. Blogging is people providing material they wish to share with whoever cares to read it. The Internet makes it possible for anyone to enter an attention market for very low cost. Attention markets have always had a lot of entrants -- many people, it seems, really like attention -- and so it's not surprising many people would start blogs. Attention markets can be brutal and cold to the casual entrant, and so it's not that surprising many people who start blogs would stop not long afterward.
If there is a sociological puzzle about blogs, it's why people read blogs, not why they write them. If blogging collapses and later comes to be seen as a "fad," it will be caused more by some steep decline in blog-reading, not a collapse of interest in blog-writing. There are many different types of blog readers, and I would love it if the sociology of the blog reader was understood better than it presently is. But: A major cause of blog-reading, as far as I can tell, is the rise of occupational circumstances that give people large amount of unstructured reading time in front of a computer. Here people are looking for very short diversions, not to watch whole television programs before they get back to work. Blogs provide a nice, brief, regular connection with another person, where that author may have something entertaining or emotional or edifying to offer you.
As for larger sociological implications, before blogs the agenda for what news stories were important and how they were interpreted was concentrated in the hands of a frighteningly small number of people given prevailing delusions about our being a participatory democracy. Blogs have helped open that up. From a System of Professions perspective, blogs are encroaching into the jurisdiction of journalists, and journalists have shown both a fascination and fear of blogs. Both reactions are deserved.