There is something missing in the data of web analytics. We know where the traffic comes from, but we don't know how it came here (beside the fact that a link was clicked on a page).
We already know what people searched for when the traffic came from a search engine, but what about the referrals. We know what domain they come from and on what page the link was, but a valuable piece of information would be to know what was the anchor text (the underlined text) of the link that sent traffic to your website.
<a href="http://www.crossbrowser.net" title="Great blog">Anchor text</a>
Think about social bookmarking web sites like Digg or reddit: knowing the anchor text of the link could tell you what people think about you. You would know if people are admiring you or laughing at you.