In our defense, my husband maintains and repairs his own bicycle, and there isn't a way to wash your hands in the garage.
You know it's a serious situation when the Magic Eraser comes away like this...
And then the cleaning wipe you subsequently use (to remove the dirty water) looks like this:
But finally your door looks reasonably clean again. (I should mention that it is a painted metal door, YMMV when cleaning a different surface door.)
Time Investment: Minimal--less than 5 minutes
Materials: Magic Eraser with water, cleaning wipe
Would I be going overboard to try and train my family to use the doorknob?