Maybe this is common knowledge, but it just occurred to me why gmail is such a brilliant idea. Google's pagerank estimates the importance of pages based on links between pages. If I think a page is important, I'll probably link to it. But what if I don't have a website to link from?
When I'm browsing the web, I'm constantly emailing people links that I think they'd find interesting. Sometimes if I'm not feeling lazy, I'll even send some blurb that explains why they should click on the link.
Until recently, Google was completely missing out on this simple and highly reliable way of guaging the importance of pages. Now that google sees my email, they can still apply 'pagerank', but some of the pages in question happen to be emails that people are sending to each other.
Frikkin brilliant. And I thought it was only about the ad revenue.