Right now, making a boat seems a bit too easy considering what it can do. On top of that, the boat's current capabilities are inconsistent with the minecarts, which have ridable, powered, and storage varieties. I think that there should be three boat types.
The first simply goes with water currents and is uncontrollable. It would appear just as boats do now.
The next, crafted by placing two sticks on the sides of a boat in the crafting grid, can be controlled by steadily pressing forwards or backwards (W or S on the keyboard) again and again. Being too wild with your pressing will result in the boat going somewhat out of control until you steady your button pressing.
The last variety of boat would be powered, crafted the same way as a powered minecart. It would consume fuel rather quickly, though, to make up for it's speed.