You know that list of checkboxes on the theme settings page that let you turn on and off parts of the theme like the logo or slogan? Well, you can add your own options to that list really easily in Drupal 7. In D6, this was kind of a pain, because you had to write all sorts of functions to save and load your settings to the database and handle everything properly. In D7, that's all done through the Form API, so the heavy lifting is done for you. All you need to do is tell it to add some form fields, and what the new setting is called!