At OpenView Venture Partners we encourage portfolio companies to do code reviews - online, not face to face. Contrary to most agile practices where face to face communication is preferable, there are some distinct advantages to online review - no posturing, no haranguing, complete documentation of the problem, leisurely review and followup.
SmartBear Code Reviewer 5.0 has some nice features and we have some reference sites for OpenView companies.
An interesting discussion on whether code review should be done before or after committing to the build can be found on the SmartBear blog.
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