John Dickson has released JCR 0.6.4 a "web application for performing and managing formal code reviews. It can be used for reviews of any type of source code, although it has some special smarts for reviewing Java projects."
My day job is pretty thoroughly committed to code reviews these days. Overall, I'd say it's a net positive. Though the review process does tend to slow down the development process somewhat, and block coding more than I'm comfortable with when the reviewers don't respond quickly, the reviews do catch a lot of serious bugs and issues in advance of check-in.