Google Calendar by itself is fine and dandy if you're comfortable living your life in your browser, but if you prefer to keep your data local and accessible when you're offline, you can take advantage of most of the great things Google Calendar has to offer without giving up your desktop calendar.
If you use Microsoft Outlook, just download Google Calendar Sync. Enter your Google Calendar username and password, and it will take care of syncing your calendar data back and forth between Google Calendar and Outlook.
The nice thing about syncing your calendar between Google Calendar and Outlook is that you get the best of both worlds.
If you're away from your main PC, you can access your calendar from any Web browser, on any computer through Google Calendar; if you're on your main computer, you can stick to scheduling with the Outlook you know and love, whether you have an active Internet connection or not.