Is this http://omeka.org/add-ons/plugins/guest-user/ the same as this http://omeka.org/codex/Plugins/GuestUser_2.0 ?
Yep! It’s just a somewhat awkward naming convention. In the documentation _2.0 basically means that it refers to a version of the plugin for the Omeka 2.x series. When Omeka 2.0 came out, we needed a way to distinguish the documentation for plugins for Omeka 1.x and 2.x, and that’s what we landed on.
Aha! Thanks for your speedy reply (as always) Patrick!