I have a gridview control that is returning rows where for 1 column the
value is usually the same. Occasionally the last couple of rows will
have a different value for this column. (2 unique values total). Instead
of displaying the same value in this column for every row, I'd like to
be able to merge all the identical values into one cell, similarly to
how I could do it in Excel.

I realise that this may be going way beyond what the Gridview is
supposed to do and if its not possible to do easily then that's fine,
I'll look at other options of providing some visial indication of a
change in that value, but I'm just wondering if this can easily be done
with the gridview (since its spot on for everything else I need it for!)

Here's a rough diagram of the sort of thing I'm looking for:

Col 1 | Col 2 | Col 3 | Col 4 |
------+-------+-------+-------+
      | Val 2 | Val 3 | Val 4 |
      +-------+-------+-------+
Val 1 | Val 5 | Val 6 | Val 7 |
      +-------+-------+-------+
      | Val 8 | Val 9 | Val A |
------+-------+-------+-------+
Val B | Val C | Val D | Val E |

The above diagram probably won't look too good if your reader doesn't
have a monospaced font - sorry for that!