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.
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.
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 }