Both my wife and I have Windows Mobile phones, and we use Google Calendar for our calendars. GooSync allows us to wirelessly sync our calendars with our phones. My wife and I both have GooSync accounts, which sync to our own Google Calendar accounts. The permissions on some of the calendars has been setup so either one of us can add events.
There appears to be a bug where events are getting duplicated, seemingly on every sync. From looking at the duplicated events, they are being created from my wife's phone. Maybe it is caused because these events were created by my account, and maybe GooSync can't handle this.