Is there a spreadsheet function that can watch a row and update a cell with the current date when any cell in that row changes? If not for the entire row then perhaps just watch a single cell?
One way of doing it, would be to use the
onEdit trigger. Unfortunately, that doesn't work. Besides that, you have to use extensive programming techniques to achieve your goal.
See the following feature request on the issue tracker: issue 200; onEdit: access original data.
If you vote, it might get introduced.
Using Google Spreadsheets, you can use onEdit.