So they finally did it. The months of will-they-or-won’t-they dissolved into years before Microsoft and Yahoo finally forged a marriage, of sorts. Reams are being written about what the deal means for advertisers, for investors and for the companies themselves. Really, though, it all boils down to one question: what will users do?

Let’s say they do create a search engine that’s better than Google – way better than Google. Will it matter? Will users use it?

Much has and will be said by Ballmer, Bartz, the media and the pundits about “innovation” and the advantages of combining two powerhouses to be greater than the sum of their parts. Perhaps Microsoft and Yahoo can pull this off. 

Google is widely regarded to have the superior product in this now two-horse race, despite Bing’s very respectable debut. Yet even combining Yahoo and Bing bring Microsoft up to only a 21 percent share of the US search marketplace, and very significantly less elsewhere in the world.  Even if Microhoo does eventually offer a superior search product doesn’t mean users will follow.

No technology company is in a better position to understand this than Microsoft, as it turns out. After all, its fame, considerable fortune and renown are centered squarely on its reputation as a software manufacturer, and no software is more central to its success than the Windows operating system. And Windows is, hands down, arguably (to many, not at all arguably) the worst OS on the market. Yet its market share, while slipping, still hovers around 90 percent.

Some will tell you Linux is the way to go, others swear by Apple. Vista has been a fiasco. IE is riddled with bugs and security holes. But Windows isn’t going away any time soon. The sky is blue, the sun rises in the East, and the vast majority of computer users just kind of expect Windows to load when they boot their machines.

By the same token, Google=search. Sure, it’s a verb. But it’s also a mindset, one as ingrained as Windows.

In blind taste tests, Pepsi has reliably trounced Coke in Pepsi Challenge after Pepsi Challenge for the past 35 years. Where the rubber meets the road it just doesn’t matter. Coke’s the market leader.

If Microsoft really wants to dominate seach, that’s exactly the mindset they’re going to have to turn around — even if they’re better.