Have a document library in MOSS 2007. Item-Level permissions are not surfaced in the default SharePoint UI for Document Libraries, however the WriteSecurity and ReadSecurity properties are available from the SPList corresponding to the list in the OM.
We have set our Document Library for WriteSecurity = 2 (only their own) through code.
When I perform a functional test on this, however, I am able to delete another user's documents.
While researching this, it looks like there is a few popular blog posts indicating that setting the WriteSecurity property through the OM should be sufficient, such as this one here:
It appears, however, that SharePoint isn't respecting this setting for Document Libraries. I've confirmed it does for at least one other list type: Links.
Is the solution to create an event receiver to do one of the following:
On the "Before" Delete/Edit events, ensure the user performing the action is the appropriate person, and if not, cancel the event?
On an Item Added "After" event, remove all permissions from everyone but the person who created it.
Also, does this story get better with SharePoint 2010?