Right front cat from our SRT6 was broken inside, and then plugged. It may depend on type of car. Turbocharged engines are notoriously hard on catalysts, and between the exhaust gas temperatures, and the full rich conditions that most turbo engines will exhibit at wide open throttle, melted and plugged substrates become the norm. On more pedestrian vehicles, so long as you care for them, and don't continuously beat the snot out of them, the catalysts will keep from plugging for a long time. Their efficacy does drop at about the 100k mark, or so, hence the way emissions warranties run out....