I frequently draft vehicles when riding through the small cities in which I've lived. It's safer to be in the traffic lane, keeping up with the flow, than to have all of those vehicles buzzing past me -- even if I'm in a designated bike lane which offers no physical barrier for the vehicles. And even on my cheap SS commuter bike, with it's cheap brakes, I can stop faster than any vehicle I'm following. And as for the OP's concern that the cyclist might not see the brake lights: are you kidding? Seriously? If a rider is that close to the vehicle, how could he miss them?