Yes, you nailed it. The flight notifications and shipment logistics are the most useful things for me so far. It's great it you have FedEx or UPS deliveries a lot, and if you travel a lot.
And you're right that you have to be comfortable with exposing a lot of data. If you have all those things you mentioned turned off, the utility of it decreases.
One problem with flight notifications: If family/friends forward you their flight itineraries just to keep you in the loop, Google Now reminds you of their flights as well. It simply scrapes for the flight data; it doesn't check the email to see if its your flight.
Not really. Last week my dad came to visit me and forwarded the airline's email with the time of the flight. Google Now correctly stated the time I should leave to catch him at the airport. Seems to work fine for me on this issue.
And you're right that you have to be comfortable with exposing a lot of data. If you have all those things you mentioned turned off, the utility of it decreases.