I\'m a huge fan of the addition of web.config transformations in Visual Studio 2010. See also Scott Hanselman\'s recent talk at MIX2011.
What sucks is that this function
If you have multiple client assemblies and don't want to duplicate the same configuration data, I created Profigurator. It'll take a JSON file as input and apply the settings to an app.config or web.config.
It's a little rough as I write this, but I am currently using it on a production system for deploys and it works great.