According to Google they "mistakenly collected unencrypted WiFi payload data (information sent over networks) using our Street View cars."
They have never admitted however how this so-called "mistake" occurred. Nothing held on private networks can have any impact on the usability of Street view, so why did the project "collect publicly broadcast SSID information (the WiFi network name) and MAC addresses (the unique number given to a device like a WiFi router) ..." in the first place? Surely all they needed was GPS and a huge disk to hold the video data.
We all know the state collects and holds private information about virtually everyone and moreover has the capacity to correlate that data across the board. Now we have it confirmed that a large public company, with a pretty dodgy record on privacy and human rights is doing the same thing.
What is building before our eyes is a corporate state of even greater power than that envisaged by Italian fascism in the '20s and '30s. Huge companies like Google or Microsoft can only exist in mutual parasitism with the state. Somehow we have to find ways to curb not just the centralising powers of the state, but the same tendency in the corporates that dominate our economic life. It may be too late of course - try searching the web without using Google or Bing, Microsoft or Apple - it can be done, but much less effectively.
You should start by securing your WiFi network! Other possibilities include anonymising proxy servers and anonymised e-mail services. Of course by using such services yoou run the risk of drawing attention to yourself, because the state will assume that anyone hiding themselves behind anonymity is a potential threat.