Wanna' Go Further or Farther?

I have this ongoing problem with two words: further and farther. 

For the most part, they can be self-explanatory. But in some instances I over-think it all. And now that I've become aware of my little issue, I've noticed it in tons of books, by writers who are NYT bestselling authors with decades of writing experience under their belts. Every misuse of these words blazes out to me from the pages now, as I've noticed with other things that I recognize as issues in my own writing. I find it causing a hiccup in my reading, because I have to analyze whether they used it correctly or not so I can push the lesson more deeply into my brain. 

Courtesy of OCAL, clker.com

Here's how they're defined by dictionary.com:

Farther:

adverb

1. At or to a greater distance: He went farther down the road.

2. At or to a more advanced point: They are going no farther in their studies.

3. At or to a greater degree or extent: The application of the law was extended farther.

adjective

1. More distant or remote than something or some place nearer: The farther side of the mountain.

2. Extending or tending to a greater distance: He made a still farther trip.

Further:

adverb

1. At or to a greater distance; farther: I'm too tired to go further.

2. At or to a more advanced point; to a greater extent: Let's not discuss it further.

3. In addition; moreover: Further, he should be here any minute.

adjective

1. More distant or remote; farther: The map shows it to be further than I thought.

2. More extended: Does this mean a further delay?

3. Additional; more: Further meetings seem pointless.

verb

1. To help forward; promote; advance: You can always count on him to further his own interests.

Reading those definitions, can you see where the confusion comes in? Even dictionary.com has included the mixed up meanings. Given, they also have this little note/disclaimer:

Usage note

Although some usage guides insist that only farther should be used for physical distance ( We walked farther than we planned ), farther and further have been used interchangeably throughout much of their histories. However, only further is used in the adverbial sense “moreover” ( Further, you hurt my feelings ) and in the adjectival senses “more extended” ( no further comment ) and “additional” ( Further bulletins came in ).

What it boils down to is that FARther really should refer to physical distance, while FURther should be referring to the non-physical. But because the words have been used incorrectly through history, we should just keep right on doing so. No wonder I've had such trouble figuring out the correct word at times!

Everyone else can do what they want--I'll be using farther to refer to the physical, not further. And furthermore, I shall continue to be confused by the use of farther when it isn't of physical distance (see definition number 2 under farther, adverb above).

Do you have further vs. farther down pat? Do you care? Does it matter? Do you use them interchangeably? What is your big grammar issue in your writing?

May you find your Muse.