Barleywine
It depends. I generally don't buy decks as soon as they're published, I wait for the buzz to settle down and for a more balanced consensus to emerge. If the book was written by the artist and not the publisher's in-house author(s), I'm more likely to want it as a companion to the deck. But, because there are so many excellent on-line resources from which to compile my own customized reference material, I typically don't spend much time with the book (or the LWB) unless it has something unique about it. In most cases, by the time I get around to buying a deck I will have to grab it in any packaging format that's currently available. (However, I will most certainly buy the RWS commemorative set since the pages of my old PKT are starting to fall out.)
