I've often thought of it as one of the primary foundations of web 3.0 (not to overuse an already overused phrase.)
Understanding how your audience interacts with your content and experiences is vital not only towards understanding how much to charge an advertiser, but also in being able to create targeted, personalized experience. The contextual web.
It must be pretty important. Adobe just spent $1.8 billion to buy Omniture an audience analytics company.