Full tank or better to drive about half full?

Is it better to keep the tank topped up to full, or should I drive around on half empty: what's better for my car and fuel consumption? Why might althletes take an ice bath after exercise? If I go out with wet hair, will I really catch a cold, or is that a myth? Do babies sleep better in a cooler room? What's the difference between an electrical blackout and a brownout? What are the consequences of high levels of uric acid in the body (hyperuricaemia)? Is the expensive face cream better than the cheaper one? Lester Kiewit and Dr Chris have the answers...