Getting to the book, my expectations about it were a little off, though I don't blame the authors for this - they did nothing to mislead. I was expecting longer essays on various aspects of games and game design. Instead it's a book, as Robin Laws put it, of "... rampaging gaming koans." If gamers had fortune cookies they ate at the end of play, then I'd hope those fortune cookies had the advice that Hindmarch, Tidball, & company offer in their little book. Saying that though, at times, I also had the opposite feeling that some of their short page statements, observations, advice, et cetera could have been expanded upon and offered as something more substantive.
One of the more interesting rpg related issues they bring up is their 29th thought: that the GM ultimately decides what sensory facts are present. Players shouldn't be penalized for a misconception or misunderstanding, and GMs need to be aware of possible vagueness in saying something like, "you hear a squeaking sound." I don't recall ever getting into a major dispute over issues like this, but I know little quibbles have constantly occurred over such problems. A role play game is a strange experience. Every player is agreeing that they are participating in the same imaginary world, but because each is a mental construct in the player's mind they no doubt form vastly different views from each other and the GM. A GM who takes her time to clarify can bring those different mental constructs closer to being the same imaginary world.
The 109th thought states that: "Whatever artistic qualities RPGs may have, they are not literary ones." (from the contributer Pat Harrigan). I don't think this is necessarily the case, but I'll hold off to write a longer post on this issue.
The book's available at the above linked site. If you're the type of person who actually goes out of their way to read a blog entitled Philosophy of Games then you're likely to also enjoy reading a book entitled Things We Think About Games.