Like you I had initial success with SP. But then I started going up and down. I started blogging about my goals and my steps to reach those goals in January. I can't believe what a difference that extra accountability made in my fitness and eating habits.
The fact is that I do not want to blog that I didn't do something I said I would do. (Nothing like putting pressure of yourself).
No matter what you blog about or how often, I am certain it can be an useful tool.