I learned this awhile back, and love it. A couple more tips about F9 in Excel:
When editing a complex formula, you can highlight a portion and press F9 to calculate just that part of the formula. This is good for testing the formula pieces without actually having to submit the changes - just hit CTRL+Z to undo the calculation.
F9 calculates the entire workbook. If you just want to calculate the current worksheet use SHIFT+F9.