I just wanted to compare different solutions used when implementing ACLs in Rails.
I use the authorization plugin (Created by Bill Katz):
Roles can be authorized for the entire application, a model class, or a specific object. The plugin provides a way of checking authorization at the class or instance method level using permit and permit? methods. It also provides english-like dynamic methods like "user.is_manager_of project" (where "user" acts as authorized, "manager" is a role, and "project" is an authorizable model). You can specify how control is redirected if authorization is denied. (quote source)
Homepage: http://www.writertopia.com/developers/authorization
Docs: http://github.com/DocSavage/rails-authorization-plugin/tree/master/authorization/README.rdoc
You might also be interested in reading this comparison (from last year but still somewhat useful; it's where I got the above quote from): http://www.vaporbase.com/postings/Authorization_in_Rails
And a more recent comparison: http://steffenbartsch.com/blog/2008/08/rails-authorization-plugins/