C# 4.0's named arguments have been introduced to make it easier to call COM components that are known for offering tons of optional parameters. If you need named arguments to improve the readability of the call to a method, that method is probably doing too much and should be refactored.

The only exception where named arguments improve readability is when a constructor that yields a valid object is called like this:

Person person = new Person
(
    firstName: "John",
    lastName: "Smith",
    dateOfBirth: new DateTime(1970, 1, 1)
);