I've got one on my Cavalier that is VERY similar to the one on Nick's Focus, and I think it looks good on the car.
Lots of Cavaliers around without spoilers on them, and the rear-end looks just too bare and 'rounded' for my taste...
My buddy has a 2008 Cobalt SS Turbo hatch, and it comes from the factory with a large spoiler, and it's one of the few features my buddy HATES about the car - makes it really hard to see out the back easily. However, I've told him he shouldn't remove it, b/c with the speeds that car is capable of (no kidding), it's pretty necessary.