Score one for the obsessive fans. Agatha Christie buff John Curran took a sabbatical from work to study Christie's 73 surviving notebooks, teaching himself to read her "bloody awful handwriting" and puzzling over her often fragmentary notes. He was rewarded with finding two previously unpublished short stories starring Hercule Poirot, the dapper Belgian who is one of Christie's most enduring characters.
The description of the notebooks in this Guardian article is interesting--a random assortment of experimental passages, ideas, shopping lists, and anything else that could be put on paper. That, and the bloody awful handwriting, sounds just like my notebooks. Out of chaos comes genius, at least in Christie's case.
The stories as well as other extracts from Christie's notes will be published in Agatha Christie's Secret Notebooks: Fifty Years of Mysteries in the Making (HarperCollins, September 2009).