Despite what some might consider questionable business decisions, including investing heavily in driverless cars and smart glasses, there's one thing Google (NASDAQ:GOOG) (NASDAQ:GOOGL) has always been able to rely on: huge revenues from its seemingly untouchable search domination. About two-thirds of Google's steadily increasing revenues are derived from search and search-related ads -- a significant figure given its $16.52 billion in total revenues last quarter alone.

But what if Google's untouchable search market domination wasn't so dominant after all? Though it's certainly no time to push the panic button, according to a new report Google is losing search market share at a rate not seen in years. There are several reasons behind the surprising drop in Google's search results, and they all raise the same question: should Google investors be concerned?

Just the facts
Analytics firm StatCounter recently conducted its annual survey of Internet search in the U.S., and Google fell to its lowest piece of the search market since 2008, and now owns a 75.2% share. Still an enviable position to be sure, and one competitors like Yahoo! (NASDAQ:YHOO) and Microsoft's (NASDAQ:MSFT) Bing would be ecstatic to claim.

But for longtime king Google, a 4.1 percentage point drop compared to December 2013 when it accounted for 79.3% of all U.S. searches is significant, particularly when it's fairly clear from StatCounter's data where the Google search defectors went -- as Google's piece of the U.S. search market dropped, Yahoo!'s took a turn for the better, jumping to 10.4% from the prior year's 7.4%, the highest search market share for Yahoo! since 2009.

As for Bing, it continues to muddle along with approximately 12% of the U.S. search market according to StatCounter. A report toward the end of last summer from research firm comScore had slightly different market share totals, but the pecking order was the same, and also noted the beginning of a slight decrease in Google's search dominance. But a more than four percentage point drop? There's a little more going on here than Internet users, en masse, opting to alter their search behaviors.

Cause and effect
Investors need look no further than the deal Yahoo! struck with Mozilla just a couple of months ago to explain Google's declining search traffic. About this time in November, Yahoo! and Mozilla announced a five-year deal to make an enhanced version of Yahoo! the default search engine for users of Mozilla's Firefox browser. The upgraded search will include a very Google-sounding, "clean, modern interface," according to Mozilla.

Not to be outdone, Microsoft CEO Satya Nadella pledged to bring Bing search back to prominence, and profitability, within the next two years. Microsoft hopes to beat Google at its own game by getting its mobile devices -- many of which are of the inexpensive, entry-level variety -- into the hands of emerging market consumers. Naturally, Bing will be the default search engine, just as Google is in all those Android OS devices.

There are also rumors swirling that Apple (NASDAQ: AAPL) is toying with the notion of ousting Google as the default search engine for its popular Safari browser, which would really hit Google search where it lives: mobile. One report suggests over half of U.S. mobile search traffic comes via Safari, and mobile is already an area Google naysayers point to as a vulnerability. No one seems to know what Apple would replace Google search with, though you can bet Yahoo! or Microsoft would be more than happy to step in.

What, if anything, does the recent search data mean for Google investors? One industry pundit isn't concerned, pointing out that the recent search market hiccup is likely a "high water mark," for Yahoo! via its deal with Mozilla, adding that, "Unless Firefox suddenly grows share, everyone who likely could get switched has been now."

Bottomline, it's much too early to panic, and Google's piece of the search pie remains dominant, regardless of whose data you choose to cite. But the recent search trends shouldn't be discounted either. With competitors like Yahoo! and Microsoft nipping at the search giant's heels, combined with its already-disconcerting decline in cost-per-click rates, there's a slight chink in Google's once rock-solid search armor.