If you snoop around the Outlook folders on your hard drive (both at
%USERPROFILE%\Application Data\Microsoft\Outlook and
%USERPROFILE%\AppData\Roaming\Microsoft\Outlook) you may see two new (to Outlook 2007) files in the folder - outlook.sharing.xml.obi and Outlook.xml.kfl.

Outlook 2007 creates these files and each Outlook profile will have its own set of files. The <profilename>.sharing.xml.obi file contains RSS subscription names. The <profilename>.xml.kfl file contains the Known Feed List for RSS which is shared with IE. If you aren’t sharing your RSS feeds with IE, you may not have the KFL file.