Why do people blog?

http://www.ics.uci.edu/~jpd/classes/ics234cw04/nardi.pdf

Five major motivations for blogging (these motivations are by no means exclusively, and can come into play simultaneously):

1) Life-documentation
2) Commentary (on environment, news, media, internet, etc)
3) Catharsis (or the purging of negative feelings)
4) Thinking by writing (using a weblog as a thinking tool)
5) Construction of community (many weblogs allow the sharing of help, support, and friendship from known and unknown readers)