>>>I don't think there should be a performance issue. Given:

>>>   public static class MyExtensions
>>>    {
>>>        public static string AddOn(this string s, string s1)
>>>        {
>>>            return s + s1;
>>>        }
>>>    }

then

string str = "Hello".AddOn(" Fred");

is just syntatic sugar for

string str = MyExtensions.AddOn("Hello", " Fred");

i.e. as far as the compiler is concerned they are identical
>>
>>
>>
>>Actually, I didn't see how there could be any performance issues either ... the guy who told me this though is usually pretty astute about such things, which is why I wondered about it. Could be that he was wrong. ;-)
>>
>
>Well, he is a man ;-)

As in, "If a man speaks and there isn't a woman to hear him is he still wrong?" :)