At last! One of my favorite rules! :-) Farther vs Further.
Farther refers to distance. (Physical)
I ran farther than you!
He can throw much farther this year.
When will we move farther away?
Further refers to extent or degree. (Not physical)
They discussed the topic much further than was appropriate.
The store's manager pushed the goals further than usual.
No further mention is necessary.
Authors/writers: Are you on my list of authors yet?