diff -r c62fa6892424 Doc/tutorial/datastructures.rst
--- a/Doc/tutorial/datastructures.rst	Thu May 17 19:49:27 2012 +0200
+++ b/Doc/tutorial/datastructures.rst	Fri May 18 16:59:00 2012 -0500
@@ -366,6 +366,18 @@
 effect with slicing and concatenation, though).  It is also possible to create
 tuples which contain mutable objects, such as lists.
 
+It may seem that tuples are very similar to lists (and they are in many ways),
+but their immutability makes them ideal for some cases that lists don't fit
+quite as well.  Though hetero- or homogeneity is in no way a programmed property
+of anything in Python's syntax or the standard library, it can be helpful to
+think of tuples as heterogenous structures, and lists as homogenous sequences.
+When used in this way, tuples are used as a coherent unit while lists are used
+one member at a time.  This is not to say tuples can only be used as a
+heterogenous structure.  In fact, there are parts of Python's own syntax that
+require a tuple that happens to be a homogenous sequence, such as the
+:keyword:`except` clause of a ``try ... except`` statement, :func:`issubclass`,
+and :func:`isinstance`.
+
 A special problem is the construction of tuples containing 0 or 1 items: the
 syntax has some extra quirks to accommodate these.  Empty tuples are constructed
 by an empty pair of parentheses; a tuple with one item is constructed by