I hate to pile on, but I'm definitely seeing the same thing. My wife has a 3G and it's solid while my 4 is struggling to load anything. Then, two minutes later, in the exact same location, my 4 will be lightning fast - her 3G the same as it always was.
I also don't have any issue with bars based on how I hold it. I run the speed tests holding it and resting on the table. Doesn't make a difference. I also don't lose bars when holding it in the normal way I usually do - maybe I just hold it strangely, maybe I have dry, non-conductive skin...who knows?
I honestly don't think what's being described here is a reception issue (that may be something separate). I think it's a software bug with how the iPhone 4 interacts with AT&T's network under certain conditions. That's my purely speculative, uneducated opinion. 😀 Hope there's a fix soon, because like most, I love this phone when it's going well.
For what it's worth, I'm in the NY City suburbs.