I totally agree a Usage Guide is not that helpful, but what I do find helpful is contextual help, especially for the back end (which I have yet to look at! - perhaps it is there already). No doubt there are tons of options, and having a bit of verbiage about some of them would likely be helpful.
A link to a page or two of introduction to the front end would be helpful to users as well, perhaps highlighting some of the key differences from the old fashioned forums.