I didn't know you tried to exchange your iPhone 4... was it because of the reception issues?
I don't have an iPhone 4, but since installing iOS 4.0.1 on my 3GS, it's been a case of "Dude, where's my bars?" It used to show 4-5 bars all the time, but now it's more like 1-3. I know it's not an actual change in signal strength but somehow it doesn't really seem like a good thing. iOS 3.2.1 for iPad apparently still uses the "wrong" formula.
Steve Jobs mentioned himself that once people know about your new product, they stop buying your old product. I can't help but wonder if he already knows that an "iPhone 4.1" is coming out in September.