Using Blu-ray as the "gold" standard, you will often see h264 streams in the 15-30Mbps range with peaks at just over 40Mbps (audio and video combined).
I've seen Netflix streams in full 1080p hit 7-9Mbps.
VUDU's HDX format will hit 10Mbps fairly regularly. They're the highest quality service I've used to date.
These services don't match physical media quality yet in an effort to work with as many users as possible. When I can stream multiple Blu-ray quality movies at once (not uncommon for a family to stream 2 or more videos to different rooms) I'll consider broadband infrastructure as "sufficient". Until then, there's plenty of room for improvement.
Where I live I could purchase service with 90 down and 9 up. Assuming I could fully utilize that (and I highly doubt I actually could which is why I've not upgraded), that could just barely do 3 Blu-ray quality streams. Not bad! However, I live in the middle of a large city, so I don't consider my options typical. I've also experienced plenty of nights where the 20Mbps service I do have is fighting upstream congestion and can't even pull 3Mbps from any video service. Not sure adding 70 more Mbps to my apartment is going to alleviate that.
So, 5Mbps will get you an average quality 720p stream. We can do better.