Minecart with Furnace

Powered Minecart
In Secret Friday Update 7, Notch implemented powered Minecarts. To create a powered Minecart you first need to have a Furnace and a Minecart, place the furnace above the Minecart in the crafting window, and you will obtain a powered Minecart. The Minecart is powered by coal.

To use the Powered Minecart, place it on a track, then select your fuel and right-click on the Minecart. When right-clicking on the Minecart, you want to face the direction you want it to travel. You can make the cart change direction by right-clicking it, facing the opposite direction of travel. No coal will be lost doing this. Destroying a Powered Minecart will give you a Furnace and a regular Minecart.

Alternatively, going up at a slope of 1/3 (two flat-rails between each up-ramp) will allow you to push your train upwards, as it appears the powered minecarts have force applied in intervals.

Important Notes

 * Breaking a "special" cart gives a plain cart and the chest/furnace back (but not fuel)
 * Powered minecarts cannot push other carts around 180-degree hairpin turns
 * A player in a cart adds significant weight, requiring more power to push
 * 1/1 (and possibly 1/2) slopes are too steep for a single powered cart to push a single occupied cart uphill. 1/3 slopes appear to be gradual enough for success
 * Multiple powered minecarts yield more pushing power; 2 powered minecarts can push a player-occupied minecart up a 1/1 slope. (although very slowly)
 * A Single powered minecart can push an occupied minecart up a 1/1 slope if there are additional minecarts being pushed. (possibly due to bumping physics)
 * When a powered minecart runs out of fuel, it does not break.