With respect, why is the /privacy/ aspect so important in a planner app that you've chosen to market it as an important feature? I actually want my planner to be public! Makes the appointments/meeting plans process simpler.
Also, while I'm not a big fan of integrating every other thing into gmail, I actually rather like that recent updates in gmail which have calendar/planner on the side, I think they've got the right idea. Something like a planner/calendar I _want_ to be ubiquitous and visible all the time in whatever UI I'm in.