I'm sure it'll be eons before it trickles down into the museum sector, but it's an interesting change:

Nielsen/NetRatings to use total time spent by users of a site as its primary measurement metric

In a nod to the success of emerging Web 2.0 technologies like AJAX and streaming media, one of the country's largest Internet benchmarking companies will no longer use page views as its primary metric for comparing sites.

Nielsen/NetRatings will announce Tuesday that it will immediately begin using total time spent by users of a site as its primary measurement metric.
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Nielsen/NetRatings will still report page views as a secondary metric, and it will continue to reevaluate its primary metric as technology continues to evolve, Ross added. "For the foreseeable future, we will champion minutes if you are comparing two sites. Going forward, we'll see what that equates to in terms of true advertising opportunity," he said.