(Note: I was tagged by Patia).
I blog because writing helps me clarify my mind - about life in Bozeman, books, movies, etc. I find blogging to be much less introspective than keeping a journal - you'll never read any stories of angst or emotional turmoil or romantic tales of bachelorhood on this blog.
I've met some interesting people via blogs, both online and in real-life. That never happens when you just write in a personal (paper) journal.
Most of the photos I post are aggressively non-artistic on purpose (yeah, right - it's all on purpose...)
I don't blog much on politics or current events. It's not that I'm apathetic - I'm just not interested in writing about such topics.
I try to be open-minded when I read other blogs. I think blogging, for many people (especially young people) is another way to "try on" ideas.
(P.S. - I "maintain" four other blogs...)