allow dragging row labels to reorder rows
The behaviour should be like the examples on http://tool-man.org/examples/sorting.html. Some notable features of that implementation are that the dragged item stays at the same horizontal position and it does not vertically go beyond the bounds of the list. I would use only row labels as drag handles, but leave dragging the text fields to mean selecting their text. To indicate draggability, up/down arrows or a Gmail-like horizontal-line grip texture should appear near the row label when it is hovered over. (You can't just use a grabbing-hand cursor because that would hide the fact that the row label can also be clicked on.)
References to other rows by label in calculations (like "R4+F5") should be updated in all rows after the row falls into its new place.