I installed my rear coilovers today. It only took 4 hours, and was a pretty easy installation. Here is a pic of the installed passenger side rear coilover.

The springs need to settle in a bit, and when they do, the car will ride a little bit lower. I gave the rear about 3/4 inch drop for now, and gave the front a 1/2 inch drop (my front was already lowered about 3/8 inch previously, so the front has a total lowering of about 7/8 inch). I can lower it more, but like I said, I want to wait for the rear springs to settle a bit, and I am going to test my road driving for ground clearance.
I want to eventually get the car as low as possible without having any speedbump or harsh road clearance issues. I can probably lower the front and rear to a total of 1&1/2 inches from the stock height in total, but I will be testing it the next few weeks at different heights to see what is comfortable.
The ride is harsher now, as the rear is stiffer now and has alot less rubber insulation in the moving parts. I tried a little maneuver where I used to be able to fishtail my rear end, but with this new suspension the rear tires didnt even break loose during the turn. Its very clear that Im going to have to flip the car around alot more violently than I used to in order to get the tires to break loose. And thats a good thing.
Next time I get a chance, I will take some high speed corners and see just how hard I can push this new suspension. I expect it to outhandle all the Japanese crap on the road today (provided they dont also have a coilover conversion), including souped up Civics, 350Zs, S2000s, WRXs, Evolutions, etc... It should give the ricers a big suprise when I do, because nobodys used to a Ford Mustang out-turning Japanese brands!