As promised, we created an animation of balloons floating in the air. They are flying upwards, because they are filled with helium and are caressed by the wind. The animation has 400 frames and was rendered in 24 hours. It would look definitely better with 800 frames and slower motion, but the render would also be twice as long. The balloons were modelled using a sphere object and shaped using Taper. The ribbons are simple linear splines.
To make them move upwards, we set the gravity to a negative value under the project settings and the value was very low, because otherwise they would be falling too fast. We added a Rigid Body Simulation tag to the balloons and a Spline Dynamics tag to the ribbons and adjusted the setting to make them move almost in a realistic way. With these settings they would fly straight up. To prevent the straight rise, we added Turbulence, which simulates the wind in our scenery. With an hour or two of tweaking we managed to accomplish this effect. The sky is made with a simple physical sky preset with volumetric clouds which also change a little through the animation.