Google has entered the bidding war over DoubleClick, the Internet’s reigning broker of graphical advertising,  elbowing Microsoft in the ribs and pushing the bidding war to a reported $2 Billion. That’s a lot more than Google paid for YouTube, but DoubleClick has actual revenue.

As many Wall Street analysts are pointing out, Microsoft can ill afford to lose the bid for Doubleclick–it’s their best remaining shot at keeping a strong position on the Web. If Google gains DoubleClick, they’ll add control of the largest flow of graphical advertising to their current position as king of text advertising. Microsoft’s only remaining play–since no one believes they can build a competitive advertising network with their own resources–would be Yahoo!, which would make $2B for DoubleClick look like an insane bargain.

Any way you slice it, a lot of money and energy is flowing into online advertising. That competition is leading to a lot more study and insight into the real impact of Web-based advertising on purchase behavior, and more advanced functionality for targetting effective ads. In fact, DoubleClick has a decent knowledge center on its own site, with various research reports and white papers documenting the role of advertising in the purchase process.  The research is certainly partisan, so read it all with a grain of salt. But there’s some worthwhile material for gaining a perspective on the current trends and spin shaping the online ad space.

Mobile ad server AdMob has raised $15M in funding in a second round led by Accel Partners, leading to anticipation of a tipping point in mobile advertising. According to Venture Beat, AdMob alone has served 1.6 billion ads in the past year, while competitor Third Screen claims to serve 350 million ads per month. While Third Screen serves enterprise clients like Ford and Fox, AdMob focuses on smaller businesses, serving a network of 1200 publishers in 160 countries. Advertisers can purchase ads across a range of mobile content channels including news, entertainment downloads and special interest communities.

The race for dominance among startups in the mobile ad market also includes Enpocket, Ad Infuse, Millenial Media, Rhythm New Media. Their business strategies range from a focus on the reach of their network, to a focus on the added value technology and services they provide to assist advertisers. Enpocket, for example, offers a range of creative services and technologies to create and target ads.

Yesterday it was PowerReviews, today it’s Aggregate Knowledge, another venture taking concepts proven on Amazon and applying them to the wider Web. Where PowerReviews is extending consumer reviews across the Web, Aggregate Knowledge is extending what they call in Information Science “genreflecting”–in this case, making product recommendations based on shared affinities with other consumers.

Aggregate Knowledge’s various ”Discovery” products work by collecting consumer behavior in the form of clicks and purchases, and then using the data to reflect back to other consumers with similar behaviors suggestions for other products and content. It’s like the popular Amazon feature “Customers who bought this item also bought….”

According to Aggregate Knowledge’s product announcement at Demo, their system was responsible for driving 20% of all products purchased at Overstock.com over the holiday season. But they’re not just pointing their engine at online retail, they’re also addressing online media, with more targetted content and advertising based on identified affinities among readers.

PowerReviews is getting a lot of buzz for a company that won’t officially launch until sometime late this year. But the company’s potential to aggregate a significant swath of consumer product reviews, and a host of user-friendly features to help customers filter through those reviews seem pretty compelling. Based on the concept of taking Amazon’s review system to the wider Web, PowerReviews will offer it’s review platform for free to online retailers, while centrally aggregating and disseminating reviews across their network. That means consumers can research a potential purchase at their favorite online store, while tapping into a much wider network of customers who have reviewed the same product at other stores. The product will be free to retailers; the company says it will earn revenue from its own shopping portal, leveraging the reviews to drive optional Pay-Per-Click traffic back to retailers.

There are a number of interesting features designed to enhance usability for posting and researching reviews, from a social tagging system to a review summary that filters up the topline takeaways from consumer reviews. One of the more interesting features is Verified Purchaser, which spotlights reviews written by consumers who have actually purchased the product in question, as validated by the retailer.

What makes this product interesting is the opportunity to consolidate a large portion of consumer review data. This would provide huge opportunities not only for advertising, but also for direct market access and research for merchants. Imagine as a merchant having a dashboard highlighting review trends and individual alerts so you can stay more closely in touch with consumers commenting on your products. Instead of having to monitor a huge number of sites, you’d have them consolidated in one place. The site already mentions the opportunity for merchants to “respond to reviews”, but the terse wording of this feature, and the otherwise narrowly defined revenue model suggest this might be a bigger part of the upcoming release than they want to announce. But now I’m just speculating.

What’s useful for marketers to consider is how to keep your ear close to the ground where consumers are commenting on your products. That’s a daunting task in a world full of vastly distributed social sites offering their own forums for product reviews. To the extent that a company like PowerReviews might draw some of those disparate threads together, marketers should pay attention.