A lot of the personal blogs are just like a digital diary, so only interesting if your into in reading other people's life. But then there are blogs that are more of a special interest, often supported by many people, and can become quite developed and useful.
Under a very loose definition of the term, this site could be considered a blog. But this is better described as a forum.
Go to Google and search "what is a blog" or "define blog" for more.