Minecarts are rideable objects placed on minecart tracks that are used to carry items, move the player faster, move automatically over a long distance, and to ride roller coasters. Wee!
Minecarts can be destroyed and reverted to a carriable item, but unlike a video Notch released if one is destroyed while riding it the player will be stuck and unable to move until reloading the level.
Minecart Riding
Minecarts can be ridden by right-clicking them, but the player cannot move the minecart while inside of it so it must already be in motion when sat in for it to go anywhere.
The minecart physics have been noted to be very unrealistic. Once pushed downhill a minecart will gain speed at an increasing rate until it reaches a cap. It also moves significantly faster/farther when ridden by a player rather than when pushed empty. An example of this is riding a minecart after being pushed up/down a slope of one block after which it will travel around an amazing 78 blocks. A player is also able to exit and re-enter a cart already in motion to keep it moving. This occurs because by the time the player has re-entered the cart, he has nudged the cart forward a little more by dropping behind it.
Anything in the way of the minecart will take it to a dead stop, including: blocks, items, mobs, and moving off of minecart tracks. When a mob touches a minecart they affect it in the same way a player would, i.e. minecarts in motion bounce away from mobs in the way of its motion and mobs that move up against a still cart will set it in motion.
Players riding minecarts are not able to move, but they can exit the minecart by right clicking it. It is also possible to interact with the environment while riding a cart, such as shooting a bow at enemies or laying down track in front of the minecart while it is moving.
The rideable minecart.
Minecart Storage
Currently the minecart cannot store any items but it has been able to in the past and it is planned to be able to in the future. In the patch update that made minecarts rideable Notch said "Rideable minecarts, but you can’t open them yet", implying that there will be only one minecart that can both be ridden and store items.
The old minecart empty.
The old minecart half full.
The old minecart's item screen.