What a coincidence - I am in the middle of this book right now.<p>It is a fantastic book backed up with tangible examples (psychology studies, mainly), and if you are in the business of persuading customers, I suggest you grab a copy. It covers most of the content from the Psychology 331 (Social Psychology) course I took at university, and is a worthwhile read.
This was one of the first books I read as a copywriter, it's a tremendous reference and because it's based on human nature, it's timeless.<p>Cialdini's more recent collaboration - Yes! - is also interesting, rehashes the basic principals, but then adds in some more current research, scenarios and applications.
I've read this book twice now. More than any other book on persuasion out there (and there are a lot now, including Sway, The Paradox of Choice, Covert Persuasion, Habit), Cialdini's is stellar. The popular Persuasion, Emotion & Trust course that Human Factors International offers is based almost entirely on this book. (So save yourself $2000 on the course... and just read the book.)<p>Keep Cialdini's "weapons of influence" in your back pocket when trying to persuade anyone -- but especially when writing your own web copy and/or creating A/B or MVT tests of your web copy. The concept of Reciprocity is one that more 'freemium' startups should be thinking of when trying to monetize.