When it comes to search, Microsoft is trying everything it can to become a serious player. It tried to acquire Yahoo, its latest version of Internet Explorer attempts to steer Web surfers away from Google, and then there is straight-out payola to search advertisers. I am talking, of course, of Microsoft’s Live Search Cashback promotion, which lets advertisers offer rebates to consumers who make a purchase after doing a Microsoft search.

After Live Cashback launched in May, Microsoft saw an initial one-month boost in its share of the U.S. search market (from 8.5 percent in May to 9.2 percent in June). But in July, its share slipped again down to 8.9 percent, according to comScore. Although we only have two months of full data (June and July) since launch to evaluate, it doesn’t look like Cashback is having any effect.

While two months worth of data is far from conclusive, it does suggest that in search you can’t buy market share. You have to earn it.

During the same period, this is what happened to Google’s and Yahoo’s U.S. search market share:

U.S. Search Market Share
———-May, 2008——June, 2008—–July, 2008
Google——-61.8%———61.5%———-61.9%
Yahoo——-20.6%———-20.9%———-20.5%

Click on the table below for a market share figures for all the major search engines going back to July, 2007