I recently added Driftwood to a couple of my tanks.
I soaked the Driftwood for week in a rubermaid container, doing daily water changes. Since I got tired of waiting for it, to stop leaching tannins, i took the risk of adding it to the tank.
Long story short, fish are loving it and the tannins haven't harm my fish in any way, only thing is that the water gets kind of brownish looking but since i do weekly water changes, it doesn't bother me.
Just make sure the Driftwood is really clean before adding it to the tank and at least let it soak for a week.