How do you use the calendar on your iPhone?

The are several ways to use the calendar on your iPhone, including syncing with other devices (including computers) and with the cloud (via a variety of services). You can also keep just one global calendar for everything, or separate ones for work, school, hobbies, family, training, etc.

• You can just use the calendar app right on the iPhone all by itself. It's not the fastest when it comes to data entry, but if you really want to keep your agenda in your pocket you can just hit the plus (+) key, add an event, and keep on keeping on (time that is).
• You can sync your calendar(s) over from Outlook on Windows or iCal on the Mac using iTunes and the USB-Dock cable that came with your iPhone. This makes sure both your desktop/laptop and iPhone calendar stay roughly coordinated (not instantly, but updated whenever you tether up and sync). Even if you intend to leave the desktop for the mobile, syncing over at first is a great way to start.
• You can sync from cloud services like Google Calendar, Apple's MobileMe, or a Microsoft Exchange server via ActiveSync. All three (if you're using GoogleSync, at least) will "push" changes back and forth between your online and on-device calendars, and if your desktop is linked to the same account, you can keep all your calendars automatically and up-to-the-minute accurate. (Pro users might even set up links between MobileMe and Google Calendar or Exchange via desktop or third party tools for cross-cloud sync). -You can subscribe to online calendars shared by others via CalDAV, which is useful for keeping track of public holidays, your favorite sports teams, special projects, or other group events on small or grand scale.

In iPhone OS 4, developers will have access to the calendar so we'll likely see movie ticket apps that automatically add the show time for you when you buy a ticket. Until then, let us know how you're using your iPhone calendar. On device, synced from your desktop, and/or in the cloud? If in the cloud, what service do you use? Any tips or tricks you care to share?