Powered Rail

The Power rail is a block added in Version 1.5. They replace bug boosting (boosters will still work after the update). It was tweeted by Jeb first to prepare texture pack makers where it will be. It will have 2 states, powered and unpowered. The powerrail was implemented in update 1.5 at 19 april 2011.

Boosting Principle
When a minecart passes a powered powerrail, it will be boosted. This will only work when you have a certain speed, powerrails will not launch your cart. If a powerrail is unpowerd, it will stop the minecart. Powerrails act like redstone wire, and will pass the power to the next adjacent rail for 9 blocks from the source.