Just to throw an idea into the mix, the mongodb reserved "_id" attribute really only applies in the context of a course currently being edited in the authoring tool (I think). It might be feasible to run those _ids through a filter to generate something that looks prettier in the browser when publishing/previewing.

Having said that, slugs have the advantage of being descriptive to the user, and the node-slug module looks as though it could handle a lot of the effort for us.