This blog related to Salesforce report folder access and permission, as of Winter '13 release.
Manage Public Reports permissionsAnyone with "Manage Public Reports" permissions can overwrite (edit and delete) anyone else reports in Public Reports folder.
Public Folder Access
Read/Write access allows user to save new report to that public folder, but not to Delete or Overwrite, even reports are created by user himself. User able to Edit the report, but have to Save As new report name.
Read Only access allows user to read report from that specific public, but not able to Save into that folder.
User with higher role hierarchy able to access reports accessible by his subordinate, although the report folder is not visible. But user will not able to Save or Save As to the same folder, user only able to Save into personal folder or public folder that he has Read/Write access.
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