Like most people, I have an IP that is unique to me, and will be for weeks, maybe months, until some event causes my ISP to assign me a new one. Google can track and correlate my activity across all the websites that I visit that happen to use GA. In this way they can build a profile. If I used Gmail, they could include information from the content of my email, which they admit their computers examine. With enough data it would be a simple matter to detect when my IP changed, and continue to amass the profile. If this isn’t spying, then nothing is.

Oh, I think I wasn't clear. I meant saying that the client is deciding to spy is a bit far-fetched. Google of course.