On Netflix blog, they post the performance they see on top ISP networks.(see here)
Currently, our top HD streams are about 4800 kilobits per second. Clients may switch through a number of bitrates as they ramp up to the highest stream, or shift down from the highest stream if they cannot sustain play at that rate due to throughput constraints. No client would sustain a 4800 stream from start to finish (there would at least be a few smaller streams averaged in for startup) but the higher the sustained average, the greater the throughput the client can achieve, and the greater the image quality over the duration of the play.
Just seemed interesting because I know that many of my clients get asked by customers, "Will that speed work with my Netflix?" We have seen it work with 1MB but more likely with 1.5MB "best effort" service.