The reason why the US will not switch from Imperial to Metric is simple. Metric is based on strict mathematical principals, Imperial is based on ease of use (not conversion)

This is under the assumption that:

1. People like units that are easy to visualize.

2. People work well with things on a scale between 0 and 10 or 1 to 100 consider:

3. People scale things with 5 being average, [6,7] and [3,4] being large and small respectively, and [1,2] and [8,9] being exceptional.

Take for example:

Distance:

Inches: One of the sections of one of your fingers is almost exactly 1 inch long. On many average people the 'rule' is that it's their thumb.

The average hand is 5 inches long, if you have a 6 or 7 inch long hand, your hand is on average big, children or small adults may have 3 or 4 inch hands.

Feet: A person leisurely walking has a 1 foot stride. A brisk walk to slow jogs run about 1 to 2 foot strides.

The average person is just over 5 feet tall (today). Tall people are 6 or 7 feet tall while children or very small adults are 3 or 4 feet tall.

Yards: A person at a moderate run generally has a 1 yard stride.

Even in the US people don't use yards for much, but in American Football a down is 10 yards.

Miles: One mile is kinda an arbitrary distance until you consider that:

The average person at a brisk walk gets 3 or 4 miles in an hour, 5 miles at a jog, and 6 or 7 miles at a run.

Pounds:

A rock that fits in your hand (baseball sized) weighs about 1 pound.

While working weak people might have problems with a 30 or 40 pound box (law requires you to be able to lift 40lbs to qualify for any type of manual labor). The average person can pick up and cary a 50 pound box around as part of his daily work. A healthy adult could cary a 60 or 70 pound box.

For laptops, you have 3lb ultra books, 5lbs for a normal laptop (but that's rapidly shrinking, mac book pros are now high 4's), and over 7lbs is considered a desktop replacement.

Liquids: In the US we use metric and imperial interchangeably. It's the one area where metric has actually stuck because wtf is wrong with imperial liquids?

Milliliter: Generally medicine is measured in ml, but normally we fill the included cup to the specified line and don't care about the specifics.

Pint: When you "Could use something to drink" you want 1 pint of liquid.

Quart/Liter: When you're "Very thirsty" you generally want a liter of liquid. Most people have no idea how much liquid a quart is these days.

Gallon: Milk is measured in gallons, and the average American family buys 1 gallon of milk a week.

2 Liter: You go to the store for a 2 liter of pop/soda. In American vernacular the "Two-Liter" is a single unit of measurement because it's easy to visualize.