This appeared today on yahoo.com and nothing could be further from accurate than this use of farther:
Confused about the difference between further and farther? Here’s what the American Heritage Dictionary says:
Since the Middle English period many writers have used farther and further interchangeably. According to a relatively recent rule, however, farther should be reserved for physical distance and further for nonphysical, metaphorical advancement. Thus 74 percent of the Usage Panel prefers farther in the sentence If you are planning to drive any farther than Ukiah, you’d better carry chains, and 64 percent prefers further in the sentence We won’t be able to answer these questions until we are further along in our research.