The book is basically a how-to on Ruling but I haven't found much on whether or not monarchs actually read or took interest in the book and Machiavelli's influence on rulers in his time.
Anybody know anything about this?
I don't know about reading and following it, but Foucault does mention in Security, Population, Territory, that The Prince apparently had more influence as a book that other writers of that time try to critique and the entire political thought and ruling was influenced by the thoughts based on criticising and being against the point of The Prince, cumulating with Anti Machiavel by Friderick the Great.
I've heard several historians mentioning that Ivan the Terrible (aka Ivan IV of Russia) had probably read The Prince. Ivan had famous personal library and is considered very close to Machiavellian perfect ruler. Ivan became Tsar at a very early age and survived through numerous schemes and conspiracies. When he came of age he turned out to be master schemer himself using noble quarrels and class divisions to gain absolute rule and weaken old Feudal system. He was also cruel and ruthless man.
Actually a similar question was asked just few days ago: