I think there is some amount of criminal element to be considered – it seems reminiscent of alerting robbers of when you are out of the house by “checking in” somewhere on Facebook. Beyond that, someone knowing your personal schedule is dangerous – this data doesn’t exist by itself, but can be added to the vast amount of data already publicly available about someone. Maybe an access-based model would be more secure. I.e. give people access to some specific span of weeks, or even the entirety of it if you really trust them, but with the added ability to revoke it or hide certain time slots / calendars. Which isn’t to say this isn’t cool, it just seems riskier than you account for.