People write blogs as a way to expressthemselves and their knowledge or expertise. People read blogs as a source of information or because they find the writer interesting. Blogs are extremely useful, both to the writer and the reader. The writer may have a lot of knowledge to share, and the reader may want an informal way to learn about a topic. Some people use blogs to find other people with similar problems, issues or situations. Blogs can be anonymous, which helps a lot of people share information without being known. Some people like to state their feelings. Kind of like your message board in WikiAnswers or talk page in Wikipedia. Same thing really.
Personally I enjoy writing and write about topics that I am interested in and that I like to write about.(I even have a blog about 'writing') Also once in a while write about products that I like, or that I am interested in 'Pre-Selling' those (Affilliate) Products, with almost all products that I (pre)sell on my blog I usually genuinely think it's about products that I believe are great products or that I have or enjoy myself. Products that It is also possible to receive comments about experiences from other people.
I write about several other subjects that have myinterest such as Travel (and as mentioned before) the process of writing itself, Movies, Music and a few other areas of interest for several of those areas I have (one or more)difaferent 'Blogspots'.
