By default the synchronization is bi-directional, but you can change this when you install the utility or from the options dialog. The only significant drawback is that you can only synchronize your main Google Calendar, but a future update should remove this limitation.
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Google installs a small program that loads at start-up and sits on your system tray, while waiting for the next synchronization (the default sync interval is 2 hours). After synchronizing your calendar with Outlook, you can access it offline and synchronize it with your mobile phone.
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It's worth noting that Google's new tool works with Google Apps accounts and it's another step towards making Google Apps more business-friendly.
{ spotted by Google Blogoscoped }