Agrippa was (and still is) a pioneering piece of mixed-media work. As well as being a book, the whole of Agrippa included an art exhibition, a live radio broadcast and, perhaps most notriously, a floppy disk containing a poem by Gibson, which self-destructed after a single use.
Broadly speaking (and horribly summarizing) the theme of Agrippa is the transience of memory - every aspect of Agrippa was intended to be as ephemeral as possible - thus the one-off radio broadcast and the one-use diskette.
The book is still around (although unbelievably rare - it is suspected that under 95 copies even exist, with 3 being held by major museums) is nearly impossible to describe, although Wikipedia does a very good job of collecting the information gained from various sightings:
The deluxe edition came in a 16 by 21½-inch (41 cm × 55 cm) metal mesh case sheathed in Kevlar (a polymer used to make bulletproof vests) and designed to look like a buried relic. Inside is a book of 93 ragged and charred pages sewn by hand and bound in stained and singed linen by Karl Foulkes; the book gives the impression of having survived a fire....
The edition includes pages of DNA sequences set in double columns of 42 lines each like the Gutenberg Bible, and copperplate aquatint etchings by Ashbaugh editioned by Peter Pettingill on Fabriano Tiepolo paper. The monochromatic etchings depict stylised chromosomes, a hallmark of Ashbaugh's work, accompanied by imagery of a pistol, camera or in some instances simple line drawings—all allusions to Gibson's contribution.
The final 60 pages of the book were then fused together, with a hollowed-out section cut into the centre, containing the self-erasing diskette on which the text of Gibson's poem was encrypted.
Happily, despite the creators' best intentions, most aspects of Agrippa have been preserved. The crowning coup in the triumph of memory is a video-capture of an instance of the diskette run. Thanks to an emulator (Apple emulators - not just for Ultima I any more!) and QuickTime, the once-elusive poem has now been captured for eternity. Or, at the very least, until the Lizard People come.