I have Comcast wifi with 150mb.
According to Netflix and Amazon, for high quality HD movies, they need a solid 25mb to stream without buffering. My movies always buffered. I called Comcast and they said that my wifi was not the #1 priority to receive the highest dowload speeds and they needed to change my billing code from "B" to "E" and change the wifi channel from channel 1 to channel 11 which now gives me the hightest download speeds. After this change, I do not have any buffering.