The search deal between Microsoft and Yahoo is finally nearing completion. On its blog today, Microsoft announced that the company’s Advertising adCenter now powers both Bing and Yahoo search results, allowing advertisers to reach almost a third of Internet traffic on the combined platform.

The deal is the next step in the 10-year Microsoft Bing and Yahoo search merger, which was announced in July 2009. Under the plan, Microsoft’s Bing search engine will power Yahoo Search and its ad sales. Microsoft will get 12 percent of revenue from Yahoo searches. In August, the two companies announced that Bing was now powering Yahoo Search.

“This will provide advertisers with the benefit of a combined marketplace through a single platform, creating a competitive alternative in search,” said David Pann, general manager of the Microsoft Advertising Search Network. “Rather than managing campaigns on Bing and Yahoo! separately, advertisers can now reach the combined audience of both search engines by managing a single account, saving time and simplifying campaign management.”

Pann predicts that ad prices may rise and fluctuate initially, but should settle into a nice groove within a few weeks. Small and medium-sized business that have a premium advertising package with adCenter will now be managed by Yahoo’s search account team.

So, how does this affect you? Well, it doesn’t, unless you own a website and use Microsoft adCenter or Google Adsense ads, or start a business and decide to buy keywords on Bing or Google. However, today’s news does mean that Google has its first viable search competitor in many, many years.