Missing referrer data in Google Analytics:
- User signs into Google account
- User searches on Google and clicks a result
- Webmaster looks in Google Analytics and sees Google as the referrer with the search phrase being "not set". If the user wasn't logged in, the phrase they used to find the site would be present.
Google states that ~10% of searches are logged-in searches (and growing), which means webmasters have a black hole in their data. Why did this person come to my site? What are they interested in? It's important to know so the webmaster can improve the experience.
But this data is available as long as the user clicked an AdWords ad to reach the site. Then it's
totally cool with giving away user behavior and information because Google got paid for it.