Commonplace Book

I had an extremely old-fashioned British English teacher in 7th grade and our biggest project was the creation of a commonplace book. I hadn't heard of it before nor since, but I still think of that project.

It seemed so random -- Page 1: recipes. Page 2: names of pet. Page 3: a family tree. And yet, it was somehow perfect. You could open any page and read something interesting. Or you could contribute some new knowledge. I feel the blogs and newsfeeds of today lack that disorganized-yet-interesting feel.

How exactly does the commonplace book differ from a journal or ubiquitous capture? Are they simply the most interesting journals of past centuries?