In an industry-rattling move, Google is today launching a test of a radical expansion of the Adwords model. The new system contains three major departures from Google's traditional advertising model:

• Ad space will be auctioned on a cost-per-impression basis. This is a first for Google, which has earned its revenue by selling ads on a cost-per-clickthrough basis.

• Advertisers will enjoy a far more granular control of their ad placements, with the ability to pick individual sites or groups of sites that correspond to keyword concepts.

• Animated banner ads will be accepted for the first time.

Anyway, Google has apparently solved whatever technical problems have prevented it from floating these features before in response to near-unanimous demand from advertisers. The second point—control of ad placement—has been the biggest problem in AdWords for years. Brand advertising on a CPM basis has not traditionally been associated with Google or any other keyword-triggered environment, and Google's foray into this realm is clearly designed to attract new species of advertiser, and large advertisers. Interestingly, CMP and CPC ad bidding will be mixed into a single auction process, with Google applying a formula for comparing the two types of bid.

More on this through the day.

Google page describing the new plan, with screen shots.
WebmasterWorld thread.