Google Inc. (NASDAQ: GOOG)'s will report its second quarter earnings today after the market close. The search engine company will most likely meet or top hyped estimates once again. Literally, Google is becoming an unstoppable force in internet advertising. With more traditional media dollars flowing to the web and away from radio and print mediums, Google stands to grow ever taller.

In June, that sentiment was proven once again as Google's U.S. internet search market share neared 70%. We're talking 69.17% of all searches performed in the U.S. -- home and business -- belonging to Google and its various tentacles. The competition lost market share as Google gained it. Although the gains and drops were small, it's all relative. A 1% drop or gain can mean tens of millions of web searches (or more).

It's taken Google about two years to come from the 60% U.S. search market share level to near 70%, as it crossed the 60% level in July 2006. The company has only grown stronger since then, and Google's advertising inventory increases as its search engine is used -- and that's how Google makes almost all of its money. It can continue to grow its revenues if it continues taking search market share. If that slows down, Google will need to step up the monetization of its other products pretty swiftly. Therein lies the Achilles' Heel for GOOG investors.