RedPhantom: that sounds familiar - maybe that's what I was thinking of.

primorge: yes, bottom book is the base (hip equivalent) and it's a vertical chain of bones.

However, I just opened Poser, loaded my pile of books, and suddenly wondered "Am I overcomplicating this?" I twiddled the yScale dial of one of the books and applied some small x/y/zRotations to them, and that appears to do what I want !

I think I should probably have explained in more detail what I'm actually trying to do. A couple of years ago I created some books as a prop, with morphs to make them different sizes. Here's some of the promo pics I did. Left is the default, mid and right are randomish size, spine-width, horizontal offset and rotation about vertical axis.

While I could make the books different sizes (cover size and spine width) with morphs, rotations were another matter. I managed to cheat by using linear morphs to produce small rotations about a vertical axis for the books in stacks, as shown above. But what I really wanted was some rotations that would tilt the covers of the books out of a horizontal plane, because that's what a real stack of books is like. I knew that I could do it by making a stack of books as a figure, but I spent ages trying to find a clever way to do it with a prop and eventually got fed up. A year and a half later I was looking at a stack of books and decided it was time to try the figure approach.

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The 3Dcheapskate (also available in DAZ and HiveWire3D flavours) occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.