The Starbucks site now has a filter to search for store locations with Google Wifi

Go to the Starbucks Store locator, and check “Free Wifi from Google.”

Here are the San Francisco locations as of 7/25/14:

Note that the listings may not be up to date. I’ve visited at least two locations that were not represented on the map but did have Google Wifi:

• http://www.starbucks.com/store/116466/us/san-antonio-el-camino-mt-view/565-san-antonio-road-28-mountain-view-ca-94040
• http://www.starbucks.com/store/15682/us/el-camino-mathilda/332-w-el-camino-real-sunnyvale-ca

A note on speed: Google Wifi is apparently 18x faster for download and 6x faster for upload than AT&T Wifi.