I too had really slow wifi on my new iphone 4S. I tried updating firmware on my
Routter resetting the iPhone with a fresh ios5. Resetting the phones network setting.
All the while my old 3G and my wife’s 3GS on ios5 was screaming along with web and videos , videos on the 4S weren’t watchable.
I tried other wifi hotspots and they all were slow except apples.
After trying all that apple replaced my iPhone, didn’t help new phone was just as slow.
So I gave up and tried a new n600 router that fixed it. Supper fast wifi now It still is like the edge at the free wifi hot spots but they are also probably running 4 year old routers like mine I am just glad it works at home and apple will probably put out a fix for it because we are not the only one with this problem. But it was unusable before with the old router I was getting .20 down and 9.20 up, now I am getting 24.97 down and 8.73 up that is spot on for my Internet speeds.