Horsepower is used as a general gauge of car performance. Although using it for such a purpose is not always accurate because of low-end torque and other factors, it is probably the most useful single number to use. The contents below are for cars sold in America. Other countries would most likely have cars with lower horsepower ratings to save on fuel, which is often more expensive overseas.
Any car that has under 100 hp is either an ultra-fuel efficient subcompact, such as the Geo Metro, or a hybrid, such as the Insight. Normal economy cars (Civic, Corolla, etc.) usually occupy the 100-150 hp range, with the 150-200 range reserved for "sporty" japanese 4 and 6 cylinder varieties (Celica, Eclipse, etc.). 200-300 horsepower is usually used for SUV's and base V8 models, such as the Mustang GT. Anything above 300 hp is generally considered a sports car. Modern cars that have such a lofty horsepower rating include the Chevrolet Camaro Z28 and SS, any Corvette, any Viper, and most Porsches, Lamborghinis, and Ferraris.