To backup your preferences and data for NetNewsWire 3.2 for Macintosh, you should backup the following:
Preferences file:
[your home folder]/Library/Preferences/com.ranchero.NetNewsWire.plist
Data folder:
[your home folder]/Library/Application Support/NetNewsWire/
To backup your preferences and data for NetNewsWire Lite 4.0 for Macintosh, you should backup the following:
Preferences file:
[your home folder]/Library/Preferences/com.ranchero.NetNewsWireLite4.plist
Data folder:
[your home folder]/Library/Application Support/NetNewsWire Lite/