It\'d be convenient if an application I\'m writing stored some files to external storage permanently (so they persist after the application has been exited[destroyed]), but
No, I don't believe so. Only files that you write to internal storage will be removed when your application is uninstalled (or if the user presses the 'clear data' button in the Application settings app).
Your app can't receive its own PACKAGE_REMOVED broadcast intent either, so you essentially have no notification that you're being uninstalled.