The only drawback being, of course, that it activates when and how the car manufacturer thinks it should, rather than how you think it should.
No more power turns, guys.
Man, movie chase scenes will really suck now. I mean more.

I cannot think of one modern car that has drum brakes.

@Bill:
What I don't understand is... in this day and age, and with so many cars out there w/ discs... how is it that drums are still a more cost-effective solution to rear-brakes?
(my new car has drums... doesn't bother me since I'll likely never go through a set of pads (hybrid))

Because some people are not smart enough to put the parking break on adequately they are going to put another expensive part to break down on the car.

@ Bill Bennett
Many rear disc systems have a built in drum for the parking brake.
It would be nice if this system can be made to apply the parking brake in response to a quick stab on the footbrake when stationary, the way some Mercedes do, which is a godsend in heavy traffic, especially in an automatic (with automatic release on application of the throttle). Whilst Slowburn is correct in that it is another expensive part to fail, I think that anyone who drives regularly in heavy (i.e. stop-start) traffic would be happy to sacrifice the cost of the odd repair for the transformation such systems can make to the driving experience. I drove in London for about three years and was eternally grateful for the Mercedes parking brake system.

@ Mel Tisdale I put it in park and pay attention to the traffic flow and don't have a problem starting on time.

What happens if your car has a dead battery and you need to apply the parking brake to keep from rolling down a hill?

My 2012 Chevy Cruze has rear drum brakes. They are somewhat more economical than disks because with disk brakes, the pads are in continual contact with the surface of the disk, whereas with drums, the shoes don't come into contact until the brake pedal is pressed.

Hill holder systems used to be popular with manual transmissions until the rise of automatics in the 1950's.
Push the clutch and brake then you can let off the brake. As you push on the gas and let off the clutch it releases the brake.
Subaru used that with manual transmissions in the 70's 80's and 90's. Dunno if they still do.

One nice thing about electric parking brakes is the lack of mechanical parking brake cables. My dad, who lives where there's road salt every winter, won't use the parking brake, because he's afraid that a road salt damaged cable will prevent it from being released.