Charley Kempthorne estimates his journal is about 10 million words long. He says daily writing helps him to be happier and healthier.
This is a wonderful piece. He mostly does his thing digitally but he prints it out on paper and compiles it into volumes after.
This article is behind the WSJ paywall but, I saved it to Instapaper and was able to read the whole thing from there. Well worth the time spent.