I know there are already threads on this, so Admins, feel free to merge if you see fit.
Here are my stats for the H&R Sport lowering springs. All measurements are from the ground to the top of wheel well, taken at the center of the wheel.
Before
Front Driver Side: 28.0625"
Front Passenger Side: 27.9375"
Rear Driver Side: 27.1875"
Rear Passenger Side: 27.9375"
After
Front Driver Side: 26.625"
Front Passenger Side: 26.5625"
Rear Driver Side: 26.8125"
Rear Passenger Side: 26.75"
Difference
Front Driver Side: 1.4375"
Front Passenger Side: 1.375"
Rear Driver Side: 0.375"
Rear Passenger Side: 0.375"
I waited until about 250 miles after installation to take the "After" measurements so the springs would have some time to settle in.
As you can see, the front is the most dramatic difference. Overall, the car looks much better. The ride quality is virtually unchanged in my opinion. I haven't driven enough to comment on improved handling, but I imagine that the lower center of gravity will slightly improve cornering and the dramatically lower front will improve turn-in.
I had my installation done at EvoSport in Huntington Beach. They did a good job. Their advice was to wait for at least a couple hundred miles before doing alignment so that the springs can settle in.