My friend Manuela suggested me "Scrum and XP from the Trenches", an introductory war story on Scrum written by Henrik Kniberg which I found very interesting.
I particularly liked the idea of a separate place for unplanned items on the whiteboard, as we normally pin them with the others, depending on the feature they address: even if the team knows why it's taking so long to get things done, the management always seems to not to. A huge cluster of unplanned items is a clear signal nobody can ignore :-)
This is another (working) example of the old bit "the simplest thing that could possibily work"... way to go whiteboard warriors!
Henrik and InfoQ provide a courtesy copy of the white paper here (you have to login first).