One of the nifty things about Google WiFi is that the app works whether you're home or away. So, sitting here in my office, I can tell you that my TiVo has consumed 24GB of data in the past week (watching NetFlix) and my home-office Mac has consumed 2.4GB in the same week (probably from the latest OS X upgrade).

This obviously implies that Google is storing this data as a cloud service, attached to my Gmail account in whatever fashion. If you've got privacy concerns with what Google can learn about you, or if you're concerned that Google might at some point become evil, then Google WiFi is clearly not for you.

FWIW, I do trust Google, largely on the strength of the people I know who work there. But also, it was super easy to swap in the Google devices, and it would be super easy to swap them back out again.