Legendary hacker and author Kevin Mitnick has produced a whitepaper in which he details several scenarios in which social engineering exposed significant vulnerabilities that lead to corporate attacks.
People who have read Kevin's books and who like his style of writing will also enjoy the paper. What I find most valuable about this paper is that Mitnick remains neutral in his approach when he outlines his "Best Practices" approach to protection. He does a thorough analysis of various techniques and methodologies for mitigating risk and locking down endpoints, while allowing users enough flexibility to perform their jobs.
People can download the whitepaper in PDF format from www.appsense.com/mitnick
It's a good read, I would recommend it for anyone security inclined even if you just download it and save it for a rainy day :o)