Nothing extraordinary with it, but it has proven to be very useful on situations where your inventory is full, or when you want to get rid of those blocks of gravel.
It consists of a block of Netherrack with fire, which will result on permanent fire. I also put a slab, that way you're not able to fall on the fire, since the head of the player's head would hit the cobble on the top of it.
Still very useful. At least for me.