Tech executive James Whittaker used to work at Google as engineering director, but left the company in February for a job at Microsoft. He’s written a blog post about his reasons for leaving, and it’s politely brutal about the company’s social strategy around Google+. “Officially, Google declared that ‘sharing is broken on the web’ and nothing but the full force of our collective minds around Google+ could fix it,” he writes. “As it turned out, sharing was not broken. Sharing was working fine and dandy, Google just wasn’t part of it. People were sharing all around us and seemed quite happy. A user exodus from Facebook never materialized. I couldn’t even get my own teenage daughter to look at Google+ twice.” The whole post is worth a read for an insight into why Facebook poses perhaps the biggest threat yet to Google’s cash cow of advertising revenues.