I use Google Calendar because it sends me SMS alerts for upcoming events, and also is pretty easy to use, on the other hand most of my work and other useful tasks are stored on Outlook, which include official calendar events, meeting reminders and more.
Google Calendar is definitely a great service and having my Outlook synced up with it really helps a lot.
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Google Calendar has a useful utility called Google Calendar Sync, that will synchronize calendar events between Outlook and you Google Calendar account. The good thing about this utility is that it supports both 1 way and 2 way communications, where changes made to your Google Calendar will be synced with Outlook and vice versa.
To start using Google Calendar Sync, download the software and add your Google Account to be synced up with Outlook. Once the software is setup it will sit in the system tray and automatically synchronize the calendars after given intervals.