I drive at least 2-3 gallon with my bearing. I only toss them out when they feel gritty or very dry. Once you cleaned your bearings, they don't seal that good anymore and the spilled oil attracks dirt.
The only bearings that I change frequently are my clutch bearing. A new set for the qualifiers, a new set for the finals and sometimes another new set if I have to run more then 2-3 finals.