Some of the pros of informational interviewing is the information that is learned will probably be accurate and from a trusted source. In this way, a person can learn what the job actually entails on a day to day basis, instead of just ideals. A person can learn a lot about how the company actually runs internally as well. The cons are the information may not be 100 percent truthful. As the book says that people like to talk about themselves, I do believe they do, but I also believe people like to stretch the truth more often then not. The information may be biased as to how that particular employee feels about the company, as well as the possibility that the answers are filtered for the company's sake. I think the benefits of the informational interview will rely solely on the person being interviewed.
Obstacles that could occur in conducting an informational interview could be finding an employee that would take the time to do it, especially in high powered industries and jobs.
Preparation for an informational interview should first be a bit of initial research on the company to show your interest in them and to impress the employers with your research. A list of questions and information that a person is interested in learning about the subject should also be thought about and prepared before the meeting. It would also be wise to have a networking card made up and ready, as well a resume to leave with the company's representative.