Is the web browser performance rule “only 2 requests in parallel per hostname” still correct?

Question

In his book \"High Performance Websites\" Steve Souders wrote (2007) that browsers limit parallel requests to a domain/hostname to two at a time. Is this still valid today?<

Answer 1

2 years later the same Steve Souders wrote in "Even Faster Web Sites":

IE8 and FF3 both increase the number of connections per server from two to six.