iFixyouri has performed a drop test with the new iPhone 4 with the Apple bumpers installed. The iPhone 4 broke after the 3rd drop on to concrete. They did not perform a similar test with a full covering case, though I suspect it is the shock from the drop that affects damage the most and a full case may not have much affect on that.
The bottom line here: Don’t drop your iPhone. If you do there are options like iFixYouri and others who do iPhone 4 repairs. I have ever used iFixYouri so I can not comment on their service.
Currently I am using the Belkin case on my iPhone 4 and have been pleased with it. It does provide an additional level of protection over the bumper only. I have been mostly pleased with the Belkin case, it does make the volume buttons harder to push, and the mute switch more difficult to swicth, but it does seem to provide a good level of protection.
Check the Belkin case out at Amazon:
Belkin Grip Vue Case for iPhone 4 – Clear
We’ve have known for a little while now that iPhone 4 bumpers do not offer all of the protection needed because customers have called in an told us. Although it does not take a video by iFixyouri to inform you that dropping your new iPhone 4 on concrete is a bad idea, hopefully this video squashed any doubts as to the bumpers effectiveness.