This screencast shows how you can use Rules to alter the presentation of your Drupal site, such as:
-Enabling, disabling and moving blocks around
-Setting HTML title element and also on-page titles
-Setting body classes
-Setting the active menu item (using Menu Position)
-Some bigger questions about using Rules for altering presentation is also discussed:
-Using Rules for presentation altering is relatively heavy. (It consumes about 2.5 MB more PHP memory than Context, and has about the same loading times – judging from a first, rough comparison.)