I was trying to figure out how to spell book art today; bookart, book-art, or book art? I'm also confused by artist book, artists book, artist's book, and artists' book. So, I did some googling to see how others spell the words (knowing full well that there isn't one standard just yet). I came across a definition of book art at encyclopedia.com , and was amused to see that they had managed to reduce the definition down to one paragraph - not an easy task! What surprised me even more was this tidbit in the definition:
<< John A. Walker (Glossary of Art, Architecture and Design Since 1945, 1973, 3rd edn., 1992) writes that it ‘refers to publications by individuals or small groups of artists whose background and training is in the visual arts rather than literature. These publications are usually small in size, slim, white, often effete pamphlets, journals, or booklets issued in small editions and marketed via art galleries rather than via bookshops … Frequently the text and illustrations are minimal and the majority are not splendid examples of printing or binding.’>>
I don't know when he added this definition of book art in the Glossary, so maybe it held water in 1945, but by the last edition in 1992 maybe the editors should have noticed that there are many artists books out there that are not "small in size, slim" or "white". As for the rest of the definition... what a jerk. (One could argue that most paintings suck, too, but that's not exactly how paintings are defined.)
For a better definition of artists books, I prefer Wikipedia's version, or this discussion on the Book Arts Web.