I started a weight loss blog on the first day I started my lifestyle change. I don't worry about my potential readers yet, because the blog is as much of a resource to me as I hope it will be to my future readers who will *hopefully* see me as a success story!!! I try to write in it every day at least once, I've already written twice today as Saturdays tend to be tough for me (it was my former binge day). It keeps me accountable in a way that logging my food for WW doesn't. Instead of just logging food, I log how I'm feeling, why I'm writing a weight loss blog, success stories of others, and inspirational quotes.
I've only been doing this for a week, but I can feel the difference this time. I need to be at least a little obsessed at the beginning. Writing in a blog daily and following the forums here religiously has helped me keep my mind focused on the loss.
I hope that this helps you, I think that blogging is a valuable tool for the writer as well as any future readers! Good luck!!