I see the chance of some numpty swinging a door on me as 1 in 1000. Doesn't sound high, but over the course of a year, I probably go past thousands of cars.
Here's one I'm glad I was on the ball with
View: http://www.youtube.com/watch?v=8WXgN5cB8WA
At the start of the video, I can see the illegally parked van. (In my experience people who park illegally are more likely to swing doors open)
0:06 a bus appears in the opposite carriageway
0:10 bus starts to overtake a second parked bus. Van door swings open
0:11 first bus has to cross onto my side of the road. There is also a taxi tailgating me at this point. I estimate the gap between the open van door and the bus to be less than 3m.
Some experienced cyclists may call this a non-event. However if I had been in the van's door zone, there is a good chance I would have been flung off the bike underneath the bus or the following taxi, with potentially fatal results.