A few days ago, I received a used copy of AMOP ordered through Amazon. This was getting to be a long-overdue stage in my development as a Lisper, because while I have written some MOP-using code (portably, thanks to Pascal Costanza's excellent Closer to MOP library), I had not yet actually studied the MOP from end to end.
One little suggestion for my fellow used-book shoppers: when a seller describes a used-copy's condition as "acceptable -- light underlining and notes in blue pen throughout," I heartily recommend moving on to the next seller. Because even though this copy arrived exactly as described, I had no idea how completely annoying it is to try to read text on the page when the previous owner has underlined nearly every single line, even in the code samples, and added little squiggles and extra notes because apparently the underlining wasn't enough! And in blue pen, which nicely stands out! Aargghh.
Anyway. Obviously, this book demystifies what the MOP is all about. Reading it gets one to thinking "hey, I could do that." Sort of the same feeling one gets while taking an operating system class in college -- getting into the nuts and bolts, one realizes that a lot of what makes up a kernel is just record-keeping (yes yes yes, there are nasty details, too). Implementing a layered architecture with good performance while preserving extensibility is a neat trick, though. This book gives me much to think about.