There looks to be an unpublish cronjob "cronjobs/unpublish.php"
and the content.ini file has the following items
[UnpublishSettings]
RootNodeList[] ClassList[]
Looking at the code of cronjobs/unpublish.php it appears that you set the root node(s) where the items you want to unpublish reside using RootNodeList[] and the classes you want to process with ClassList[]
The items you want to be able to unpublish need to have a date attribute with the identifier "unpublish_date" - this is checked against the current date.
I've tried what Bruce has suggested and it seems to work OK. You have to add a datetime or date field attribute with the identifier 'unpublish_date' to the classes you want to use this for. I wasn't able to get the unpublish event working by setting up a workflow to unpublish items.
