It has always been my understanding that all moral and attractive people observe the distinction that says "farther" refers to literal distance ("Brad Pitt is standing no farther than ten feet from Ben Affleck") while "further" is reserved for conceptual or metaphorical uses and matters of degree ("Watching a Ben Affleck movie is the furthest thing from my idea of a good time.")
It turns out, though, that the venerable Oxford English Dictionary, while acknowledging this distinction, says that there are many instances "in which the choice between the two forms is arbitrary." And even the famously persnickety H.W. Fowler (of Fowler's Modern English Usage) was uncharacteristically wishy-washy on the subject, maintaining that it was just a matter of individual preference, and that eventually "further" would carry the day for all instances. Harumph!
I like the idea of different words performing different functions, so I'm going to continue to acknowledge a difference, and to question the character of those who don't.
