QUICK HIT: 7 Trillion Impressions for Google Web Fonts
The Fonts within Google's free Web Font Library have been seen over 7.6 trillion times.
Google provides some analytics on the fonts within its library which highlight not only the total number of font views, but the number of views per font in the past 7 days, 30 days, 90 days and one year, and eve offering up some data points on how specific font use changes over time
Google also provided a font view distribution by browser and operating system. That's useful as it shows designers which fonts are most common on specific devices and system setups.