Here's a pic of the back of my Speck Fitted case I got at AT&T yesterday:
I doubt it would give a lot of protection if dropped from any great distance; I wouldn't be surprised if it did come apart. Plus, there's not a lot of "padding" to help with impact protection, and there's one large cutout at the bottom for the connection and speaker, and a cutout with no button covers for the volume/mute buttons.
However, it works for me, since I'm pretty cautious, and was just looking for something that would give me a better grip and protect the back without adding a lot of bulk. If you work or play in more rugged areas than I do, you may want something a bit tougher.
I didn't notice any problem with the flash, but I've only taken a couple of flash pictures with it (I just got my iPhone yesterday). The black color probably helps negate any flash distortion.