This post will improve and change as the site evolves. Some things those posting albums will want to consider (this may change as I figure out how to reconfigure the Gallery module):

• You may want to go to the "Gallery" link, and under your default gallery, go to "Edit Permissions". I would suggest adding the following two permissions under the "Group" section:
  1. For Group "Everybody", add the "[comment] View comments"
  2. For Group "Registered Users", add the "[comment] Add comments"
• Use the "Make Highlight" option to choose the thumbnail that will be used for a particular album.

UPDATE 7 June 2006:
You can add comments to blogs, forums and pictures (provided the album owner did the two steps above). When you are actually viewing either an album or picture click in the "item actions>" drop-down, pick "Add Comment". It's pretty obvious where to add comments to the other areas.