Minecraft wiki entry for Minecart, associated text: Minecarts appear to float above the track, as their model has no wheels.
If the player views their inventory while riding in a minecart, they appear sitting down in mid-air.
The player can teleport to another minecart while sitting in a minecart by right-clicking a minecart in their range. This can be used as an elevator to quickly rise up when minecarts are placed on top of each other.
If the sound is muted in the options while riding a minecart, and then turned back up, the minecart no longer makes noise in the client until the player exits the minecart.
If a saddled pig is riding a minecart, the player can ride the pig. Doing so causes the minecart to be able to ride freely at the player's walking speed. It is unknown whether this is a glitch.
It seems that hunger does not deplete while inactive in a minecart (at least in normal difficulty).