When I got my Forbidden Lands group together, I gave them each a little kraft travel journal; you can get 12 packs pretty cheap on Amazon (I got Blue Summit brand), and they look exactly like the type of notebook an adventurer would stuff in his/her backpack before setting out on a journey. I figured they'd come in handy if the players wanted to make notes about adventure sites, encounters, monsters, etc.
But by the end of the first session, one player had already filled a few pages with in-character journal entries, and another player went home that night and compiled his notes into a journal as well. The third player, who was initially less inclined to use the notebook, eventually succumbed to the others' enthusiasm ended up doing something similar. (He's playing a peddler, so it's mostly about the great swindle he perpetrated.)
So the notebooks have been a really powerful tool for helping the players develop their characters and their enthusiasm for the game. I definitely recommend it to other GMs, especially if your players are the creative types.
By the by, I posted this on Reddit, but I wanted to share it here as well.