Google recently refreshed its list of the top 1,000 sites on the web.The sites are ranked in terms of unique viewers, based on data gathered by Double-click Ad Planner. Google explains how this advertising service determines a website's weight: "Double Click Ad Planner combines information from a variety of sources including anonymized, aggregated Google Toolbar data from users who have opted in to enhanced features, publisher opt-in anonymous Google Analytics data, opt-in external consumer panel data, and other third-party market research."The top 1,000 list is far from definitive, though. Google has left off specific kinds of websites, such...