At what speed does Aerodynamics of a bike come into play? Is a more aero bike more efficient than less aero bike at 10mph? At what speed does Aerodynamics affect your speed significantly. 

update: "The question is dealing with the minimum speed that a cyclist will notice the effects of a modern aero frame vs a non-aero frame. via @user"
As long as you are moving through the air, aerodynamic drag will account for some portion of total drag. Here is a plot that shows the relative contribution of aerodynamic drag vs. rolling drag on total drag for a rider at constant speed on a flat surface with the given CdA (drag area) and Crr (coefficient of rolling resistance). There is no magic threshold speed at which aerodynamic drag suddenly appears. Whether the amount of drag is important or significant to you will depend on your power and riding goal, but for this example roughly 25% of total power will be consumed by aerodynamic drag at about 10 km/h (or about 6 mph).