There is a bug in umbraco that causes the deletion of uploaded files embedded in a document type after the deletion of copied content nodes (see http://umbraco.codeplex.com/workitem/27419 and http://our.umbraco.org/forum/core/general/9669-Nasty-bug-when-deleting-copied-content-nodes-with-an-uploadFile-property for details).
This package contains an event handler that prevents the deletion of uploadField files when there are other content nodes in Umbraco referencing them.