By popular demand, we've published a Houdini Foundations book [www.sidefx.com].
Written by SideFX product expert Robert Magee, it's a 100-page book directed at artists getting started with Houdini and its node-based procedural workflow. Even though it covers foundational topics we think Houdini users at all levels will find it useful as reference - plus it has a keystrokes map on the back cover which is useful for everyone.
The PDF is available for download now, and we'll be printing some to distribute at GDC. The plan is to sell it through an online ‘print-on-demand’ bookstore. Details to come soon!