When I finally get to sit down at night, just before bed, I like to treat myself to a chapter. In it, a given artist will reveal his/her approach to sketchbook journaling, and describe methods and favorite materials. Several pages from their sketchbooks are shown (my only criticism is that these reproductions are too small).
One thing that has struck me is that each artist (so far) has expressed in one way or another a similar idea. That is, that recording scenes from life - even if it's something rather mundane - helps them to really "see" things around them. It helps them to find "quiet" and results in firmly planted memories. Each page will bring back a flood of detailed rememberances - where they were when they drew it, what they were feeling, etc. - even if many years have passed.
My sketchbooks have often been a place for me to practice some skills or work out the mechanics of certain images. But, now I'm a little more inspired to treat it more as an illustrated journal. Or, like one of the artists, keep the practice work for a "crappy sketchbook" and have another to treat as an art book/journal. I'll certainly try to have it with me more often and to look at things around me a little differently. This could be fun!