Remember a few years ago when people talked about how many "hits" their Web sites got? Now, we look back and think how quaint things were in olden times, when pioneers were just beginning to settle the Wild Wild West of the Internet.

Someday, we might feel the same nostalgia for page views and impressions, because new technologies are muddying the metrics picture.

Why? Here's one example. Yahoo is rolling out a redesign of its home page, which the company modestly calls "the world's most visited Web page." One of the main features is an AJAX (define)-powered "personal assistant," which sits on the top right hand corner of the page. The assistant lets users interact with their e-mail, Yahoo Messenger, LAUNCHcast Radio, Yahoo Weather, Yahoo Local, and more without leaving the portal's home page.

The company told ClickZ that designers placed an ad unit directly underneath the assistant because it expects users to spend a lot of time there, but it's not clear how this will be quantified. Surely when it call itself the world's most visited home page, it's talking about visits, that is, page views, which generate ad impressions. What now?

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