Jakob Nielsen talks about the "About Us" page:

"Saying who you are and what you do is basic politeness in any conversation. In business, it's also good to establish credibility and respect by explaining your company's origins, how you view your business, and how you relate to the community.

The Web is very depersonalized, but from our earliest usability studies, we've seen that users like getting a sense of the company behind the website. Who's there behind the screen?"