In Netflix, you can also go into your profile settings on the web site and force the highest quality streaming all the time rather than have it throttled back if that's what you want. Even at HD levels, the streaming speed is about 7 Mbits/sec, which is using some heavy compression if I recall correctly so most internet services can easily handle this.
Netflix will soon also offer Ultra HD (3840 x 2160) for one program series but I don't have a device to check this out on yet. Very few people do at this point. That will tax the network more but not sure how aggressive their compression will be for it.