Nielsen//NetRatings' elevation of time-spent over page views as its primary Web metric in July was generally applauded as a step toward improved audience measurement in a Web 2.0 world. Agencies and online publishers alike welcomed the new standard as a better gauge of online activity in the wake of technologies like Ajax and streaming video that let users linger on sites without reloading pages.

"For us to hear this from Nielsen, my response was, 'It's about time,' " says Jeff Lanctot, senior vice president for global media at Avenue A/Razorfish. In its Digital Outlook Report issued earlier this year, the agency featured an article titled "The Death of the Page View," which predicted marketers would begin eschewing the page view in favor of other measures including time-spent even before comScore or Nielsen came up with a replacement.

The biggest immediate impact of the move was Google's being dethroned in Nielsen rankings by AOL. But the page view isn't about to disappear as a benchmark, and online ad spending won't change overnight as a result of the switch. In a blog post about the Nielsen move, JupiterResearch analyst Emily Riley noted the advertising world is still deeply tied to the page view. "With less than one in five online advertisers even measuring 'engagement metrics' such as time-spent, the transition away from page views on the advertising side still seems far off," she wrote.

For its part, the Interactive Advertising Bureau isn't ready to anoint time-spent as the new de facto standard for comparing Web sites. "We have to be careful that we're really looking into all options to come up with the most accurate definition of what engagement is and then come up with the most transparent metric for it," says Sheryl Draizen, senior vice president and general manager of the IAB.

To that end, the IAB is developing new industry guidelines both for Web audience measurement and for counting ad impressions in the context of "rich Internet applications" such as Ajax, widgets and RSS feeds. The IAB expects to provide preliminary guidance on audience measurement by October.

The standards for determining when ad impressions are counted on sites using Web 2.0 technologies are expected to be finalized and released by mid-August. The IAB has long pushed the major Web audience rating firms to be more open about their tracking methods. Nielsen//NetRatings and comScore in May agreed to timetables for the auditing of their technologies and processes by the Media Rating Council.

Lanctot says advertisers will ultimately have to take an increasingly holistic approach to Web measurement. "In the end, you're not going to see any one metric rule the day," he says. "Smart media players are going to take into account a number of factors in making buying decisions."