It be just your particular setup. I just went out and tried my 4S using bluetooth audio streaming to play some music and it was good. I didn't try and make a phone call since it sounded good with my music.
I am having the same problem with audio streaming using bluetooth with data dropouts occurring about 6 times an hour. With iOS 5 I would only hear a data dropout once every couple of hours. I powered my iPhone 4S down to see if that helped but didn't see any difference. Using my headphones there is no data dropouts occurring.