Dive summary:

• Interactive Advertising Bureau (IAB), the online industry's largest trade group, is pushing for "viewable impressions" to replace "ad-impressions served" by Q1 2013.
• The metric would count only impressions that were viewed by the user, instead of all impressions served even if the user never gets to the section of the page containing the ad.
• One item up for debate is what length of time constitutes a view.  Sherrill Mane, SVP, industry services for the IAB said, "We are proposing a minimum of...one second.  As we go forward, we will learn about how that impacts different kinds of ad formats."

From the article:

The largest online ad industry trade group is pushing for new ad metrics to become standardized by the first quarter of 2013. The primary goal: begin to phase out reliance on the ad impressions-served metric and replace it with the viewable impressions metric. Also by that time the Interactive Advertising Bureau and its partners in the initiative expect advertisers and publishers will be using the eGRP metric, which industry players hope will complement the viewable impression metric with a more audience-focused gauge that speaks to brand advertisers.