Not many, it's not as necessary if your right foot is buried on the gas pedal. It's the stick shift guys that have to lift on each shift that really need it. When the throttle is closed immediatly after being under boost, the air has nowhere to go as the intake upstream of the TB is still pressurized. This puts an additional load on the turbo bearings, hence the need for a blow off valve to vent the pressure. With an automatic the tendency is reduced considerably. Just don't go from wide open to zero throttle all the time and you won't have any issues. BOVs do sound cool at times......annoying at others.
