The study used the very scientific method of quizzing 300 men and women, ages 15-50, about hypothetical situations (taking back a promise, not visiting a relative in the hospital, snapping at a friend) and women displayed significantly higher levels of guilt.
Men do feel guilty about something, though. Overindulging. They felt the most guilt about self-centered situations that affected only themselves. Too bad another study found that people who felt guilty about indulging in life's little pleasures had weaker immune systems!