Excerpts from http://online.wsj.com/article/SB117271649934522912.html 

Bumpers on most midsize cars do a poor job of protecting the vehicles
from damage in low-speed collisions, and the cost of repairs following
minor fender-benders can be surprisingly steep.  

Formerly one-piece steel bumpers are now integrated into the vehicle's
front-end design. This happened in part because new rules don't
require bumpers to be as strong and protective. That means consumers
wind up paying thousands of dollars to fix damage from even a minor
collision.

Even the best performers in the tests wound up badly bruised. A 5 mph
impact on the front bumper of the top-ranked Mitsubishi Galant
resulted in $929 of damage. A similar crash inflicted $3,911 of damage
on a Subaru Legacy, $4,535 on a Nissan Maxima and $4,594 on a
Volkswagen Passat.  

In the tests, each car collides with a steel barrier that is shaped
like the front end of a car and is built with a wide plastic cushion
and a flexible cover similar to the energy-absorbing bumpers and
bumper covers on most cars. The institute recently redesigned its
crash barriers to look and respond more like the bumper of another
vehicle instead of a flat wall. The full test includes four impacts:
front and rear full-width crashes at 6 mph and front and rear corner
bumps at 3 mph.

The Nissan Maxima, Pontiac G6 and Volkswagen Passat each sustained
damage estimated at more than $4,500 in the frontal test. These cars
have bumpers that slid underneath the barrier, allowing their bodies
to absorb much of the impact. The costs reflect damage to the cars'
hoods, fenders, headlights and even air conditioning condensers
mounted just behind their front grilles.  

Rear-end tests showed similar patterns of expensive damage when the
cars' bumpers weren't tall enough or were mounted too high or low to
properly engage the barrier. The Hyundai Sonata performed best in this
test with $739 of damage, mostly limited to the bumper. Cars' front
bumpers generally were not wide enough to prevent extensive damage in
corner impacts. The headlights of all 17 cars were damaged in the 3
mph corner impacts. This is because the bumper bars aren't wide enough
to protect those parts.  

Many cars appear to have bumpers that wrap around their front corners,
but the underlying bumper structure is rarely as extensive as the
cover. On many cars there is empty space behind the corners of the
bumper cover, so headlights and fenders tend to wind up absorbing the
energy of the crash.

Consumers also may not be aware of the differences in the cost of
repair parts from one vehicle to the next. The Toyota Camry needed
extensive repairs after the rear crash test damaged its body panels
and trunk floor. The cost of the repairs was $1,480, which is low
compared with some other models that cost more than $3,000 to repair
because their parts are more expensive than Toyota's.