Well, I'm very apprehensive as well.
I do have an iPhone 4 and previously an iPhone 3 (not s). I've seen my signal strength drop abruptly several times on my iPhone 4, but never drop a call. This was typically in sections that I expected low signal strength and even poor phone quality (below-ground parking garage, elevator, etc). My phone performance is (subjectively) exactly the same as my old busted iPhone 3. I still experience the same amount of call degradation in spotty areas. So, even though my reported signal strength is a little lower than expected, I still experienced my previously expected performance of the 2-year-old model.
I really don't know which side of the fence to toss my 2-cents in.