Default values for meta tags are not used

I believe you will not see this when creating the node. Did you check the source? What is produced when the page is constructed?

Yep, they're intentionally left empty to avoid having to save OG data for a node unless it overrides the default values. With the main tags the description tell you why they're empty. I think I just need to add descriptions to the contact and location tags clarifying this matter.

Fixed in 6.x-1.x-dev.

This works perfectly 'as designed' in the 7.x-1.1 version, really cool!

The only thing I can't get to work is og:description.
It seems to get the node:title by default, but I want to have it use the meta description that is generated by
http://drupal.org/project/metatags_quick

RDF Mapping that meta field to og:description doesn't seem to have an effect. (override by Open Graph Meta tags module?)

Added a new hook in latest dev release: og_tag_render_alter

Documentation in opengraph_meta_test_module.module

/**
   * Implements hook_og_tag_render_alter().
   *
   * @param $node the node whose tag is being rendered.
   * @param $name the name of the OG tag being rendered, e.g. title, image.
   * @param $value the value of the OG tag being rendered.
   *
   * @return the altered value to render for the given tag.
   */

Perhaps this will suffice?

Changes will available in the next release.