I think it's safe to say that Google's an Internet giant now. Google sites have surpassed 1 billion unique monthly visitors, based on comScore data for May.
Take that, Facebook. Actually, take that, Microsoft. They're number 2, followed by Facebook, Yahoo, then Wikmedia.
That's globally. comScore's Media Metrix top web properties in the US looks a little different, with Yahoo leading the charge, followed by Google, MIcrosoft, Facebook, and AOL. Here's the top 50 for the US:
Of course Google's presence is felt well beyond its websites, through every Android device used, every use of its Chrome web browser and/or Chrome OS, and every page where someone has embedded a YouTube video. Then you have all of the sites using site search, Google Apps, etc.