I am highly enamored of the board book as a structure. It's essentially the same structure as a "book dummy" in which verso/recto spreads are glued together to form a remarkably ugly simulation of what your book will look like. The difference is that the stock used is heavy, so the glued-up pairs for a fairly sturdy piece of cardboard.
these things are often done for kid's books, in which case they include a remarkably clever bit on the back so that the cover will work correctly given the complete rigidity of all the parts.
I love these for photos, because the photos don't flex.
Does anyone actually use these things in, uh, "real publishing"?