Just this past month Bing gained more of a percentage of market share than any of the other major search engines – up more than 22% from July, according to Nielsen. With Google’s perennial firm grasp on the #1 spot, this leaves Yahoo! and Bing to duke it out for numero dos…and Bing is gaining ground fast.

Until now, if you were thinking about expanding your search engine marketing campaign beyond Google AdWords, Yahoo Search Marketing (YSM) was the natural consideration; Bing (Microsoft Ad Center) not as much. But Bing just became a whole lot more appealing.

There’s a minimum amount of overhead required to start up and manage a search marketing campaign…and for some industries Microsoft’s search engines (MSN and Live Search) have traditionally not offered enough eyeballs to justify the time required to manage an ad campain on their platform. But as it gets closer to matching the number of searches on Yahoo!, Bing becomes more appealing to advertisers, and ad prices across all three of the top search engines could become a bit more competitive.