For anyone tempted to think that there's a "right answer(TM)" here(1) 
(2), I recommend Kent Pitman's classic:

       http://www.nhplace.com/kent/PS/EQUAL.html

(1)  I'm not accusing anyone of so thinking.
(2)  I mean that there's no universally right definition of equality.  
Of course, I do NOT mean that it isn't possible to write a correct  
program for a given domain that uses some kind of equality test.