I'm about to hook into this this morning. I have a fair way to go with the ride height. I'm lowering the fronts more by shortening the shock length from the bottom. Due to the design of mine, the rears can only be shortened by the spring, but there's a fair whack of travel.
Main concern with lowering coilovers for me is ensuring that there's no bottoming out (which can occur if you lower it solely with the springs, some cars don't have this issue though, others do due to their designs I've noticed.)
Just to clarify, I've heard horrid stories of the above at certain suspension shops who are... wewy spethal in the head lol.