I've kept an engineering notebook for years. It was something I was told to do in college. It seem that the act of writing down the problem slows me down enough to focus my thoughts more on the task.

I've tried keeping notes on the computer and they are useful. But, I've never gotten the same level of focus from writing in an online journal. I wonder if the focus comes with practice. I type much faster than I write longhand, so perhaps I lose the trigger of slowing myself down.