Due to popular request, I will now delve into a sticky situation to many, namely further vs. farther.
Farther should be used when discussing distances, when referencing a measurable amount of miles or kilometers or whatever.
For instance, "My house is farther east than yours.
Further should be used when talking about something more nebulous, a relative amount of something, generally not distance-related. For example, "You have to read further in that book to get to the good part." This example means that you'd have to advance in the book from your current page to get to an interesting bit.
Similarly, people often misuse "less" and "fewer". Fewer should be used when talking about something that you can readily count. For example, "I have fewer books than you."
Less should be used when you're discussing something that cannot be counted individually. "I drank less water today than yesterday" would be an example. Water isn't something that you can count individually. It's a mass quantity.
If you ever see those express lanes at the grocery store that say "12 items or less", that's not correct. If you're feeling particularly jerkish, you should demand they change it to the correct "12 items or fewer", since items are something that can be counted individually.
There are some exceptions, of course. It sometimes gets tricky with time and money. "That movie was less that an hour and a half" is acceptable, even though hours can be counted individually. Also, "I made less than $100 this week" could also pass as correct. But the phrase "fewer dollars" is ok but it's "less money". Dollars can be counted but money is a mass amount.
Confusing sometimes, eh?