In the section "Initial User Synchronization" you describe the need to map the users. I am doing initial testing with the first option of only 3 users. You say that they "need to be manually mapped". I didn't find anything in the gallery site admin web tools to do this. I also searched the forums and didn't find anything. I used mysql commands to add an entry to the g2_ExternalIdMap table to accomplish this. Is this the correct way to "manually" map a user? Could you include a short section describing the tables to edit?
Also the http://cvs.sourceforge.net/viewcvs.py/gallery-contrib/embed/ link is broken. I searched sourceforge and i find a gallery-contrib item. It contains stuff from the google 2005 summer of code, and doesn't seem to include anything like you are referencing
In the "An entry point" section: You have a link "Integration - How to write new integration code" (http://codex.galleryproject.org/Gallery2:Integration_Howto#Writing_New_Integration_Code) which contains a section about "Changing integration code from Gallery 2.0 - 2.0.2 to Gallery 2.1 compatible integration code". Could the sample code in sample_embedding_wrapper.zip be modified to include the proper 2.1 format of the GalleryEmbed::init call? The 2.1 version could be in a comment below the current version.