I was thinking about this. I'm not sure how the other sites did it, but I would try to write an algorithm that classifies whether a page has an event or not. I

I was thinking about this. I'm not sure how the other sites did it, but I would try to write an algorithm that classifies whether a page has an event or not. If there is an event, then parse it and check for duplicates. I have some other ideas for easily allowing users to add events.