After so many years of the Castle Project never making an RTM/GA release, DynamicProxy with Castle Core is the first project after the split to hit the gates running with a gold release.
You can head over to sourceforge to download 2.1 RTM if you so choose. However, the key part of this release is to allow projects like the Castle MicroKernel to RTM with a released DynamicProxy.
There were several minor changes made between 2.1 RC1 and 2.1 RTM, see the Changes.txt for more details.