title: overhead to unused "using" declarations?
body: <p>I've just installed resharper and it's letting me know the namespaces i'm not actually using in each of my classes.</p>
  
  <p>which lead me to the question - is there actually any overhead in leaving these, unused, using declarations in?</p>
  
  <p>is it just a matter of tight code, or is there a performance hit in invoking these namespaces when i don't need to?</p>