
Digg beats Flickr and breaks into the top 20 web sites in the US.
Alexa Internet is a California-based subsidiary company of Amazon.com that is best known for operating a website (www.alexa.com) that provides information on the web traffic to other websites. Alexa collects information from users who have installed an Alexa Toolbar, allowing them to provide statistics on web site traffic, as well as lists of related links.
Alexa ranks sites based on visits from users of its Alexa Toolbar for Internet Explorer and from integrated sidebars in Mozilla and Netscape. There are several third-party extensions for Mozilla Firefox; these extensions do affect Alexa rankings. Because only a small procent of people use the toolbar of the extensions the Alexa rankings are considered as inaccurate.
Source:
Alexa