Note taking has been a little, helpful hobby to me. I loved taking notes in class—lettering, organizing, doodling in margins (that counts too!) At work, I keep a notebook documenting my daily tasks and meetings. Though I am not as systematic as MIT professor, Ed Boyden, I enjoy his blog entry ‘How to Think’ that praises the note taker. [thanks for the link Carl!]
Here’s my collection of artists’ notes. via Smithsonian Archives of American Art

Ray Johnson note to Eva Lee.

Notes on painting from Oscar Bluemner’s ‘Theory Diary’ 1919-1920.

Many figures in a group, notes above., ca. 1943 / Antoine de Saint-Exupéry.

Gio Ponti to Esther McCoy.

Notes on Greta Garbo, between 1930 and 1950 / Nickolas Muray.