Netflix accounts for more than 20% of downstream internet traffic during peak times in the US

"Netflix's roughly 16 million subscribers [update - now 20m] can access streaming content from a variety of devices - XBox 360, iPads, laptops (and that's just in my household). And that adds up to a substantial increase in demand. A recent study has found that Netflix makes up more than 20% of downstream Internet traffic during peak times in the U.S."
Source:  ReadWriteWeb, 21st October 2010