The using statement (or Imports statement for VB.NET) affects performance in the IDE but not the execution of the code. When the code is compiled, the compiler will use the using statements to resolve where to find the different classes. The more using statements you have, the more checking it will do. For VB.NET, there is even more of a performance hit since it has background compiling that C# does not offer. Once the code is compiled, all the references have been resolved and the code will not perform any differently.
