Minecraft wiki entry for Development_versions, associated text: Allows an entity to stay on it for 1.5 seconds (30 ticks), before the entity will fall through it.
The tilt happens in 3 stages: unstable, partial and full.
All the stages are solid except the full stage, which is when the player falls through.
When nobody is standing on it, it is set to none stage.
Comes in two sizes: small and big. Small can be applied bone meal to grow into big.
Small Dripleaf can only be obtained with shears (otherwise breaks), and can only be planted on clay or underwater on clay and dirt blocks.
Big Dripleaf can be obtained with any tool or by hand as well as breaking it using projectiles and can be planted on grass and dirt blocks.
The tilt can also be triggered by hitting the plant with a projectile.
The tilt can be prevented by powering it with redstone, but hitting it with a projectile still tilts.
Available under Experimental Gameplay.