The practice of writing zibaldone, or collections of notes in paper codices of small and medium format, such as we might call commonplace books, began in the mid 14th century. The word means "a heap of things" or "miscellany" in Italian. The earliest such books were kept by Venetian merchants. The keeping of such notebooks at this date might have been associated with the availability of paper at affordable prices by this time.
"Rather than miniatures, zibaldone often incorporate the author's sketches. Zibaldone were in cursive scripts (first chancery minuscule and later mercantile minuscule) and contained what Armando Petrucci, the renowned palaeographer, describes as 'an astonishing variety of poetic and prose texts.' Devotional, technical, documentary and literary texts appear side-by-side in no discernible order. The juxtaposition of gabelle taxes paid, currency exchange rates, medicinal remedies, recipes and favourite quotations from Augustine and Virgil portrays a developing secular, literate culture. By far the most popular of literary selections were the works of Dante Alighieri, Francesco Petrarca and Giovanni Boccaccio: the 'Three Crowns' of the Florentine vernacular traditions.These collections have been used by modern scholars as a source for interpreting how merchants and artisans interacted with the literature and visual arts of the Florentine Renaissance" (Wikipedia article on commonplace book, accessed 01-16-2011).
Regarding the Zibaldone de Canal, illustrated in the photo attached to this entry, see Dotson, John E. (editor and translator), Merchant Culture in Fourteenth-Century Venice: The Zibaldone da Canal, Medieval and Renaissance Texts and Studies, Binghamton, New York, 1994.