Here are links to the complete "How to Propagate Ficus Benjamina with Water Rooting" saga:
Part 1, Part 2, Part 3
It's really easy, all it takes is a little patience, some sunlight and basic houseplant stuff. It's a great thing to do with kids too, shows them how plants grow. Might not be as fast as a potato, but it lasts a lot longer and is more satisfying in the end. Heh.