We just put out a small maintenance release of Review Board 1.6.5 tonight. This has a couple small changes that may be useful to users of Git or the web API.
The biggest change, however, is that it actually will install properly on new installations. The Django project just released their version 1.4, and Review Board 1.6.x is incompatible with it. Now, we hard-code the latest compatible version of Django.
If you recently tried installing Review Board on a new system, please try removing your version of Django 1.4 and install Review Board 1.6.5.
Release notes are available.