Set a CCK field to only have one value on one node across whole site - all other nodes will have no value for that field.
Tick a checkbox on a node to make it featured somewhere, when the checkbox is ticked on another node it will unset the value on the first node. Use in combination with Views to set up a featured event, news, or any other type of content - can also be used to exclude the node from other Views generated listings.
Drupal 6 version has support for the Synchronize Translations module (i18nsync). If a field is set to be synced across languages then the value will be exclusive to the source node and it's translation node(s), other nodes will be cleared of their value.
Drupal 7 version has only been tested with a boolean field set to display as a single checkbox, should also work with other fields but at the moment untested.