Common ways you get dents

Supermarket Trolleys

Probably the number one cause of dents is that frustrating trolley dent from the supermarket. Heavy shopping and trolleys that have a mind of their own together with heavy traffic trying to find places to park can mean people aren't always watching where they are going. Because most car parks are designed to maximize the amount of cars, the space between cars means that the likelihood of picking up trolley dents is higher.
Hail

Believe it or not, one of the most common causes of dents to cars is completely natural. Particularly strong hail storms can cause body damage to most types of car. Most modern cars in order to keep the weight of the car down make the body out of lightweight materials that in heavy storms is more susceptible to hail dents.
Driver Error

There are more cars on the road and unfortunately there are more distractions from people using mobile phones to a car full misbehaving children. Whatever, the case, driver error is something that happens and occasionaly you will have to fix either dent caused by a driver who just wasn't concentrating properly.
Vandalism

Vandal damage eg. kicked door panels is unfortunately a part of everyday life and is usually the product of heavy drinking and antisocial groups. Vandalism tends to be more of problem in the built up city areas.