I own the GHD and it changed my life! It is super-easy to use, and the effects last for days! I've been using it for over a year and a half and still get compliments on my hair! It literally turns my frizz-prone, wavy hair into spun silk.
The important thing to remember, though, is to use a good heat protectant. Not only does it minimize damage, but it helps the iron glide over your hair more easily and holds the style. My absolute favorite is Redken Iron Silk. It get my hair straighter, holds like nobody's business and prevents frizz.
I have thick, curly, color treated (aka damaged) hair and I love my GHD Pro Styler. I've gone through 5 or 6 flat irons in the past few years and this one is by far the best. It heats up in 10 seconds and even turns itself off after 30 minutes. You can also curl your hair with it since it has beveled edges. Overall, AWESOME!