The biggest challenge to the Microsoft-Yahoo search partnership may not be Google the company as much as Google the habit.A recent analysis conducted by research firm comScore states that Microsoft-Yahoo is in a good position to increase its search market share and lure more advertisers, but will have a hard time competing with Google user loyalty.This loyalty manifests itself every time you hear someone using the word "Googling" as a synonym for "searching." To disrupt all the Googling, Microsoft-Yahoo will have to offer a compelling reason for users to break the habit.One obvious way to do this, according to the comScore report, would be for Microsoft-Yahoo to simply create a better search engine than Google. Another way would be to integrate Microsoft-Yahoo search with Microsoft's applications and online services enough to distract users from Google. A third way, of course, is to market and advertise more than Google. Microsoft is already doing most of these things, but Google's search numbers are still daunting. As of June 2009, Google sites had 65 percent of searches in the United States, and Microsoft (8.4 percent) and Yahoo (19.6 percent) combined had 28 percent.ComScore also conducted an analysis of search loyalty and found that, not surprisingly, Google searchers have the highest loyalty rate. These users conducted 69 percent of their searches on Google sites. While Microsoft-Yahoo search engine users conducted 32.6 percent of their searches on Microsoft-Yahoo sites, a much higher 60.7 percent searched via Google sites.But although Google has a comfortable overall search market share lead, the percentage of searcher penetration (amount of actual users searching, but not the amount of search queries) is much closer. The combined searcher penetration of Yahoo-Microsoft is 73 percent, not far behind Google's 84 percent.The reason for the discrepancy between searcher penetration and search share is that Google searchers simply conduct more search queries on average in a month (54.5) than searchers on Microsoft-Yahoo sites combined (27).Microsoft-Yahoo could turn this trend around by keeping users on their sites for repeated searches. "The challenge will be to create a search experience compelling enough to convert lighter searchers into regular searchers, which is generally easier than converting new users," says Eli Goodman, comScore search evangelist, in a release about the report. "Though clearly easier said than done, if they [Microsoft-Yahoo] were to equalize the number of searches per searcher with Google they would command more than 40 percent market share."Nevertheless, Microsoft-Yahoo will have to do battle with a brand burned into the brains of billions of people: Google. "The challenge facing a Microsoft-Yahoo combined search offering is that choice of search engines is often a subconscious decision on the part of the user," says Gord Hotchkiss, CEO of Enquiro Search Solutions, a search engine marketing firm. "For Microsoft-Yahoo to disrupt the Google habit, they have to offer a compelling enough reason to do the cognitive heavy lifting required to break a subconscious habit."Are you a Tweeter? Follow me on Twitter at twitter.com\/smoneill. Follow everything from CIO.com on Twitter at twitter.com\/CIOonline.