I had it and hated it. It's not really any kind of protection. It won't protect the iPad from even a small drop, and it's not even rigid enough to shield the screen from impact. It doesn't protect the back at all.
I am currently using a Targus 360 case, and it's better. Front and back protection, quite thin, and allows me to stand the iPad in landscape or portrait mode.
I sold my Smart Cover, and I do not miss it. I will, however, be modifying my Targus 360 with some magnets to get the sleep/wake function and stronger connection when closing the cover.
And I would never put Ghost Armor or an Invisible Shield on my iPad. The glass is exceptionally durable and scratch-resistant, so there's no point to doing the front. The back NEEDS it if you're using the Smart Cover, but that doubles your expense. You can get a single good case that protects the back and front, or you can cover your iPad with plastic and then put a Smart Cover over that, for twice the price of a single cover.
I just don't think it's a very elegant or useful accessory. Your mileage may vary.
I just know I wouldn't want to drop my iPad with only a Smart Cover protecting it.