cut springs are not the way to go, but its not the horror story everyone is saying.
you can cut a 1/2 a coil and it will still ride ok. 1 coil is the limit IMO. never cut more then 1 coil off a spring.... any spring.
cutting a spring shortens it (we all know this) but the problem is that taller springs are usaly softer and allow more travel, softer ride, etc. when a soft spring is cut (to lower the car) the spring is no longer tall enough to keep the car from bottoming out and bouncing. this is why buying a shorter 'performance' spring is far better. the shorter spring has a higher rate and even if the car is lower it bottoms out less (or never).
ive heard of heating springs, but ive also heard it messes with the rate, the spring becomes too soft. but ive not lowered anything this way. i lowered an older chevy truck by cutting the front springs and blocking the rear. it worked really good. but not as good as buying the proper lowered spring, and it was a big truck, so handling was never high on the list.