I posted this in another SGP thread, but I thought it was relevant here too. I'm using the SGP Ultra Crystal screen protector on the front.
I got my white leather and black carbon fiber weave SGP Sking Guard backs in today. Overall, I really like them. I didn't realize how thick they were though! Should be very good protection for the back of the device. I've included pictures below of each with my Black Apple Bumper installed. There is no issue at all with interference from the Bumper. Both textures feel really authentic. The carbon fiber really feels like carbon fiber (and may really be, I can't tell), as does the leather.
One thing I can tell is that the white leather, although it looks really good on the phone now, is going to get VERY dirty. The texture just feels like it's going to collect all the dirt that comes into contact with it.
Also, the cut outs are perfect, but they are pretty close. I don't like how tight the camera and flash cut-out is, because if it's off even just slightly (like my carbon one is), it will throw off the alignment of the cut out for the Apple logo.
**Also, the white leather DOES have the issue where the camera flash interferes with picture taking. The black carbon does not. I assume it's because the white color is more reflective of the flash's light.