Farther or Further?

Some writers/speakers use "further" and "farther" interchangeably. Others are insistent upon the following:

• Further is used to convey a measure of time or a degree; in some cases it is used in place of "additionally" or "moreover"
• Farther is used to convey distances.

It's a good idea to distinguish between the two meanings by using further and farther as defined above. That way, you will please your total audience: those who care about the further/farther usages and those who do not.