Would be great if there were the ability to have content in a cell that you
wanted to footnote to add the footnote through a wizard tool. You could
launch a footnote wizard which would allow assign a footnote (and superscript
number following the cell content) and create a footnote associated with the
cell which could be included below your spreadsheet as a movable object. If
you clicked on the cell it would highlight the footnote and if you clicked on
the footnote it would highlight the cell(s) associated with the footnote.

I know that are cell comments but they aren't very useful for displaying
content in a printed form to annotate or footnote a spreadsheet when showing
and noting finacials. This is done by finance and accounting groups all the
time when they prepare financials for presentations.