"... do you feel that code reviews should be mandatory"
- The answer is "Yes". Code review is systematic examination of computer source code intended to find and fix mistakes overlooked by programmer(s) in the initial development phase. Code reviews can often find and remove common security vulnerabilities such as:
- Format string attacks,
- Race conditions, and
- Buffer overflows.

Software repositories, like StarTeam, allow groups of individuals to collaboratively review code to improve software quality and security.

Code Complete, Second Edition (Paperback) by Steve McConnell, Microsoft is a good source of on how to perform code review.