I recently added in a timed automatic logout to an application that pays attention to user interaction as well as Authlogic's lastrequestat magic field. If you just need the user to be automatically logged out after 15 minutes and it's ok to have them kicked out on the next request then the native functionality within Authlogic will work great, take a look at the Authlogic::Session::Timeout section in the documentation.

DownThemAll! gives you ability to download all assets on a page but it currently doesn't support downloading resources within external files like stylesheets.