If you constantly work between Outlook and Google Calendar, then this is an excellent plugin that enables you to combine the best of both worlds.
Of course, Outlook has features that Google Calendar doesn't and vice versa so this program truly allows you to combine both to get the best out of them. OggSync is a simple utility that synchronizes appointments, events, tasks, alarms and much more. Whether the two products synchronise successfully depends largely upon whether you get the configuration right which can take a few attempts - it requires a little bit of a trial and error approach. One particularly big benefit of this program is that it extends many of the best features of Google Calendar to Outlook. For example, in Google Calendar I have different calendars for different areas of my life - work events, family events and leisure. Normally, Outlook doesn't allow you to do this but by using OgSynch, it brings a whole new wealth of features to Outlook, including the ability to separate events in this way and even to Windows Mobile devices.
A truly useful utility for those that spend way too much time between two calendars and need to simplify the way they organise their lives.