This is my suggestion of an implementation of min/mean/max computation
in columnview summaries. If you like it feel free to use it.

New operators: {min}, {max} and {mean} possibly prefixed with : for use
with timevalues.

Example from my running exercise diary:

#+COLUMNS: %DISTANCE{+;%.1f} %HEARTRATE{mean;%.1f} %SPEED{:min} %CALORIES{+}

Gives a colview with summaries:

total distance, mean heartrate, fastest speed (min/km) and total
calories.

I have tested it on emacs-23 and it works well for me now, also with the
interactive colview functions.

But you never know really. ;-) Anyway, there should not be any emacs-23
specific elisp code added afik.

(Because I do not use xemacs I have not tested it with xemacs but the
small changes I made should be compitable to both xemacs and emacs. I
would appreciate if someone on this list who uses xemacs will give it a
try for me. Thanks!)

(This fix also opens up for using user defined lisp functions to
calculate colview summaries, but I am not sure if that is something
useful. Like this:

(defun std (&rest values)
  "Compute standard deviation."
  ...)

#+COLUMNS: %DATA{eval:std}

If someone finds this attractive it would now be easy to implement as well.)

doc/org.texi               |    6 +++
lisp/org-colview-xemacs.el |   87 +++++++++++++++++++++++++-------------------
lisp/org-colview.el        |   87 +++++++++++++++++++++++++-------------------
3 files changed, 104 insertions(+), 76 deletions(-)

I have attached four small patches, one for each file changed and the
last one for all changes.