It happened to me a few years ago when I hit a pothole and the mech bounced sideways into the wheel. Hell of a fright.
Hmm.. thinking about it - and this may be complete coincidence - I 'may' have just ridden over a bit of hard plastic that the wind blew in front of me. (it's like a wind tunnel down that section always in your face).
Just trying to price up some bits now.
Edit: Facebook rocks. Friend just offered his bike on loan till I sort mine, coming around in 15 mins. Awesome. Not such as emergency now.
As I ride to work every day, I will still need to find a cheapish bike to replace it, or find a cheap way to repair it. A rear hanger by itself is £15 to £20 (The hardest bit to obtain I would imagine).