For now, however, most advertisers say the short-term metrics give them a good sense of advertising ROI, particularly for specific campaigns with clear objectives.
"We don't specifically look at one metric," said Kate Price, director of corporate direct marketing for Oracle Corp. "We look at click-through to cost per registrant to conversion rate."
Oracle has been using new online ad formats recently proposed by the Internet Advertising Bureau, including vertical skyscraper ads and larger ad formats.
Larger, Flash-based units achieved a 25% to 30% higher click-through rate than regular-size banner ads.
"There is the opportunity for more of our message to be included, and it's more interesting," Price said.
However, Oracle declined to be specific about campaigns. Indeed, most of the marketers contacted for this story declined to give out any hard numbers.
Analysts agree that while advertisers can realize short-term results from new ad formats, their long-term benefits are unclear.
"There is a novelty factor, since they are larger and more dynamic," said Christopher Todd, an analyst at Jupiter Media Metrix Inc.
What's more, these ads may change the way users interact with them. "Because they contain so much information, users may not feel compelled to click on the ad. It's all right there," Todd said.
This may mean that the click-through rate, originally considered the key metric of online advertising, may become even less informative in the future.
Steve Carbone, managing director for Grey E.Marketing, New York, said an integrated approach works best for b-to-b clients, and cautions against concentrating on just one medium.
Grey E.Marketing's average response for banner ads alone stands at 0.5%, direct mail alone at 1.5% and e-mail alone at 11%.
But in combination, as part of an integrated campaign, the three media offer much higher returns. "When we use direct mail, e-mail and banners, we've seen a 22% response rate on the b-to-b side," he said.