I'm not sure how we draw the line. But it should at least feel ethically itchy if ppl can use data you collected to statistically infer things normally considered private information.

This puts Google on the wrong side of the line, wherever it is, next to other big offenders - fb, twitter, linkedin.

To waffle less, I would absolutely be very cautious with who you give access to your gcal. You can tell a lot about a person knowing their schedule, who they meet with, where they meet, when they fly, etc. Lots on a calendar