I would also recommend you consider augmenting this system with one or more of these additional features:

1. A default configuration file;
2. Added: A database-resident collection of configuration settings; this would necessitate database connection information be in one of the other mechanisms on this list;
3. Environment variables which override the default config file;
4. A command line switch to specify an alternate configuration file, which overrides environment variables and default configuration file entries;
5. Other command line switches which override any other settings.