I am using resharper to do a big refactoring and i keep going from file to file and adding the same namespace over and over again in the \"using\" section
Open ReSharper Options / Languages / C# / Namespace Imports
Add "Namespaces that should always be imported"
Run Code Cleanup against solution or project. You may want to create profile (Options / Tools / Code Cleanup) with only Optimize Using Directives module.