I'm pleased to announce that we have posted a release of Sandcastle that now supports the MSHC Help file format used by Visual Studio 2010.
The MSHC support was commissioned from ComponentOne, whom we thank for updating the code base to support this new Help format. We have additionally rolled in a variety of bug fixes since the last release in 2008. Please note the MSHC Usage Notes and Changes/bug fixes documentation links on the download site.
MSHC support is currently limited to reproducing the VS 2008 look and feel and functionality within the VS 2010 Help Viewer. To achieve parity with VS 2010 look and feel will require more work and we encourage enterprising folk out there to take this on and contribute to the code base.
See also the Sandcastle blog here.