Here are some links to help people get started with importing, exporting, editing, converting or animating MMD models in Blender:
MMD tools is the only add-on which allows you to import a VMD animation into Blender ("initial support" for VMD export has recently been added in powroupi's version of MMD tools). You should definitely use a recent version of Blender with this add-on because multi-threading was added to Blender in Blender 2.77 which allows you to run a preview animation at a much faster speed than was previously possible. The experimental version of MMD tools in the master.zip file allows both importing and exporting of .pmd and .pmx models. The older stable release versions of MMD tools don't allow exporting of models.
Blender MMD Tools add-on
MMD tools Github page:
MMD tools master.zip direct download from Github:
MMD tools older stable releases: