A whole new world of minecarts awaits us in the upcoming redstone update, in which you will, apparently, be able to place Spawners, TNT and Dispensers in minecarts.
This is going to be perfect both for natural world traps (as in, naturally generated pitfalls generated by the same world generator that failed to give us Herobrine, and for multiplayer servers, where you’ll never be able to trust a minecart rolling down the rails ever again.