On Jan. 13, Nielsen offered up its December 2009 data for the U.S. search market, finding that Google held 67.3 percent of that market, with Yahoo following at 14.4 percent and Bing in third with 9.9 percent.

Granted, this is just one research firm's report, which will most likely vary from reports by other firms, but compare those December numbers against the ones from November 2009:

Google: 65.4 percent

Yahoo: 15.3 percent

Bing: 10.7 percent

According to Nielsen, both Yahoo and Bing seem to have lost ground to Google heading into the beginning of 2010. It could be a monthly fluctuation. But it could also be perceived as a potential problem for Microsoft, when you consider that November-December timeframe saw the company launch a whole host of new features for its search engine designed to bring it into more direct competitive alignment with Google.

If Yahoo's percentage is also falling, then that potentially spells trouble for the success of the Microsoft-Yahoo search-and-advertising agreement, which was supposed to radically boost Bing's market share in 2010.

Specifically, I'm talking about features such as the beta version of the new-and-improved Bing Maps, which introduced an option for viewing local terrain at eye level, and a new Bing Bar for Internet Explorer and Firefox.

In conversations with Microsoft spokespeople at the 2010 Consumer Electronics Show (CES), I was given the impression that Bing's engineering team would continue to refine the search engine throughout 2010. No doubt some new features will be rolled out, as well. But if data from other research firms comes back with a similar dip for Bing, and if that incremental downward trend continues through the first months of the year, then Microsoft may need to think very hard about what it needs to do to continue the slow search-related momentum it managed to build over the course of last year.

What do you think?