I became interested in code reviews while working with Accenture Ireland. As part of my role I was responsible for introducing code reviews into the project and insuring that they took place.  It was amazing to see the difference a 15 minute discussion of a piece of code or a design document could improve the overall quality of the project.  As more people are aware of the design for an early stage.  It also serves to educate more junior developers on the team.  Srivaths Sankaran presents a good overview of code reviews in this article.  It will give you a good background in to why we perform Code reviews and the many aspect of a code review.   He concludes his article by saying:

…..You can conduct thorough code reviews without succumbing to time pressures. Did you know that more than 60 percent of the defects can be captured by effective use of peer reviews (c.f., Boehm and Basili's Software Defect Reduction Top 10 List )? With a judicious combination of automation, interactive tools, and risk-based evaluation, you can reap the benefits of early problem detection…..

One piece of advice I would say is to remember that the primary goal of Code reviews is to improve quality and educate developers.   It is not a witch hunt!