I started using Event Calendar as-is a few years ago when I started developing websites for the churches I attended with WordPress. Today EC3 has become a focal point on our website at Calvary where I am on staff as an Associate Pastor.
The key features to EC3 are its simplicity, it is post oriented, and all of this makes it seemless on the website but with loads of extensability. Currently I am posting all of our church programs and events through the calendar. I am using the PostLists plugin to add lists of events to the bottom of our program pages (still in development). In the future all of our Sunday sermons will be podcasted with the podcasting plugin but show up in the event calendar on the dates that it was preached. Want to catch the sermon you missed from last week? All you would have to do is click back on the date you missed and find the sermon in the post along with notes and powerpoint etc.!
All of this is compounded with some awesome people coming on board making this one of the most useful plugins for WordPress in my opinion!