Microsoft's "new approach" to tracking the effectiveness of online advertising can be read as a broadside attack on the way that Google makes most of its money: search ads.

We've seen this coming for a while. Brian McAndrews, formerly CEO of aQuantive and now Microsoft's top advertising strategist, foreshadowed what the company is calling "Engagement Mapping" late last month. He wrote that "the current system for tracking ad conversions, while the best available for years, is not optimal because it gives all credit to that last ad seen or clicked -- often a search engine -- and not any credit to other ad units the consumer may have seen prior that helped influence the user to seek more information about the advertiser."

Presumably, Engagement Mapping will correct that inequity by accounting for "all the various online touchpoints and interactions a consumer experiences before an eventual sale." So if you see a banner ad for a Honda Prius on a Web site and then search for "Prius" in Google on your way to finding a dealer and buying a new car, this system could give some credit -- and revenue, I'd guess -- to the banner ad and perhaps take some credit away from search ads. That could increase the banner ad's value for both advertisers and the publishers who sell space on their Web sites.

The system will measure and account for data about a consumer's contact with ads, including recency, frequency, size and format (such as rich media and video) and how each ad channels the consumer toward a purchase. The tool itself, about which Microsoft provides precious little detail, will be called Engagement ROI and available as part of the Atlas Media Console -- a technology for advertisers that Microsoft acquired as part of aQuantive. Starting March 1, a group of customers will try out the beta version of Engagement ROI and Microsoft plans to have results before the end of June.

ReadWriteWeb has some good discussion of where this effort fits among the broader changes in how the Web and people's interaction with it is measured for commercial purposes.

My question is how would this system account for off-line sales and advertising such as billboards, TV commercials or, in the case of consumer packaged goods, a product's place in the store? (Think of how often you reach for an item that's at eye level vs. the stuff down by your feet.)