Approaching this book as a reader who is not a musical performer and has only very basic understanding of reading musical notation, I was a little bit trepidatious. I needn't have been though, as 'Piano Notes' is an enjoyable book full of anecdotes and insights into piano techniques, performance and repertoire, and any lover of classical music will get a lot from this elegantly written book.
The stories Charles Rosen weaves into each themed chapter often involve the famous names of twentieth century pianism (Horowitz, Richter, Gould etc), and he brings privileged and often quirky information into them - from the strains of memorising works, to the importance of how high (or low) the piano stool is set. I also found the chapter on recording classical music very interesting, in which he discusses both the technicalities of splicing different takes of one piece, and the artistic problems inherent in doing so.
My overall opinion then is that this book is accessible enough for non-specialists, and anyone with an interest in classical piano music will thoroughly enjoy it.