I've been working on Malevich - my code review system - on and off for almost 5 months now.
It turned out to be very successful - my team was using it for all of our first milestone, and was very happy about it (we're now pushing 1500 change lists that went through the system). Many other Microsoft teams adopted it since, to the tune of at least a couple hundred people - and these are just the people who contacted me.
The biggest problem so far was the setup. The deployment was hard - it required Visual Studio, a service pack, an expansion pack, and tons of manual work. A lot of errors were made, and in many cases I had to drop by and set things right afterwards.
Not any more! The first official build is out, and it has a real setup! The setup checks the dependencies, deploys the database, publishes the web site, and configures notifier automatically, no Visual Studio is required!
So if you wanted to try Malevich but were intimidated by the complexity of installation - the wait is over. You still do have to install Server 2008 with IIS and SQL Server 2008, but the rest is done for you.
Just get the MSI here: http://malevich.codeplex.com/Release/ProjectReleases.aspx?ReleaseId=26374
Happy code reviewing!