What is everyones opinion on the use of fuel additives, especially in today OHV OPE engines?

Example:

Lucas Fuel Treatment

Lucas Fuel Treatment

A powerful blend of oils and additives that contain no SOLVENTS. Designed to increase power and fuel mileage and also lower exhaust emissions through a more complete combustion. 

Lucas Fuel Treatment is formulated for both gasoline and diesel engines, carbureted or fuel injected. It gives your fuel system what it really needs - a blend of super slick oils and additives with a high detergent action that allows the engine to operate at maximum efficiency. Also, it cleans and lubricates the carburetor and injectors and causes the fuel to burn more thoroughly for increased power and less fuel consumption. Lucas Fuel Treatment should definitely be used in vehicles that require leaded fuel because it actually replaces the benefits of lead in gasoline without causing harmful emissions. Use it to pass smog tests. Finally, it totally neutralizes the harmful effects of low sulfur diesel fuel.

Key Benefits

• A great tune-up in a bottle
• Cleans and lubricates the fuel system
• Neutralizes low sulfur fuel problems
• Increases power and miles per gallon by burning excess exhaust emissions
• Increases the life of pumps and injectors