For me, it's mostly because I enjoy the topics that I'm writing about - I have a passion for them, I enjoy sharing what I've learned and learning about what other people are thinking of the same subject. If I can help someone discover something or spark a conversation about a thought, then I'm very happy.
My blogs are pretty wide-reaching, from the one you're reading (my main blog) to the Baker Street Blog, about one of my literary interests, to Nothing Could Be Finer Than Being in Your Diner that I write with C.C. Chapman.
So it's pretty interesting when I find something that encompasses more than one of the subjects that I write about. In this case, it combines my interest in Sherlock Holmes with Twitter (which, if you aren't a user, has been experiencing a lot of down time lately):
Via Hugh McLeod.If you blog, I'd love to know what motivates you. Why do you keep doing it?