How to: Add and Remove Web.config Settings Programmatically SharePoint 2010

How to: Add and Remove Web.config Settings Programmatically SharePoint 2010
http://msdn.microsoft.com/en-us/library/bb861909.aspx

http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.administration.spwebconfigmodification.aspx
http://didierdanse.net/blogs/dev_en/archive/2009/09/11/sharepoint-how-to-use-spwebconfigmodification-class.aspx