Many property pages of a project (File --> New --> Project --> Web Application Project) support Configuration specific properties:
What this essentially means is that all the properties in that tab can be saved in the project file and will be saved per configuration. This would mean that when your active configuration is "Debug" then all the "Debug" settings will be used.
Debug and Release configurations are available by default inVisual Studio but if you would like to add more build configurations (for various server environments like “Dev”, “QA”, “Staging”, “Production” etc then you can do so by going to the Build --> Configuration Manager.
You can also select your active configuration for Visual Studio 10 from the Configuration Manager UI as shown above.
The configurations are stored in the project file as shown below:
Note: Deleting a configuration for the solution does not delete it for every project within the solution and visa versa, so when using Configuration Manager make sure that you remove the configurations from the correct locations
Hope this helps...