Two metrics determine how much money Web sites make from advertising: page views and unique visitors. The number and character of “uniques” — that is, how many separate and distinct individuals visit a Web site and how much they are likely to spend on products being advertised — determines the cost of ads on a Web site. It’s the page view, however, that governs how much money Web sites take in for ads sold at a given rate.

Today, Web 2.0 technology threatens to knock the page view off its pedestal. AJAX (Asynchronous Java-Script and XML) and Flash make Web pages more like desktop applications, enabling users to interact — filling in forms, browsing through options, and so on — without loading pages. The obsession with page views now stands squarely in the way of a vastly improved user experience: The more user-friendly the Web page is, the less revenue it produces for the host site.

There is a solution to the problem. Sites can log AJAX and Flash events — defined as any user action that would normally result in a page view, but does not, thanks to enhanced functionality. Google Analytics, for example, lets Web developers assign a page file name to any AJAX event, which is then counted as a page view.

The problem for Web sites and their advertisers is that no standard method yet exists for logging events. Advertisers can’t be expected to delve into code and normalize how AJAX and Flash events are logged. So last December, comScore Networks, one of the top Web metrics clearinghouses, announced that sometime this year, it would be releasing “enhanced measures of user engagement and advertising exposure” that would include events.

Page views will remain a useful metric as long as HTML persists. But the march of Web technology is diminishing the importance of old-fashioned “page views” — and making way for more accurate measures of user interaction.