My 50mm 1.8 wasn't so lucky. It took a direct hit with a frisbee when filming a frisbee golf commercial, and the lens broke into pieces. If you're going to break a lens, this is the one to break.
Mine too, it cracked like a raw egg after a fall - after this experience I vowed to get better gear and get an idea how much beating it can take - thus this thread.
L lenses are built to have superior image quality, not to to bounced off the ground.
:-) but it still gives some comfort to me reading these reports, because usually I'm transporting my gear in bike bags which is rather inconspicuous and does not say "here comes the photog! I'm the one to steal from!". But it of course it doesn't protect the stuff as well as a real bag.
Is the IS especially prone to break after a fall, and does it make any difference if it is switched on or off on transport?
The quality of construction of the L lenses is definitely better, its not really about plastic or metal, since the grade and quality of the plastics is different for more expensive lenses. However, you can destroy a lot of 50mm f/1.8 lenses for the cost of repairing one 50mm f/1.2.
Check out Tokina Lenses, they are built like a main battle tank, I'd select them for their build versus cost if I were carrying them where damage was likely. Sometimes the build and ruggedness outweigh a tiny bit of IQ difference, and they are pretty good in any event.
If you have a lens mounted to a camera in a bicycle bag, its much more likely to be damaged, the attachment on both the camera and lens is aligned to amazingly tiny tolerances, and can be bent out of alignment easily. Then you will not be in focus from side to side or top to bottom. Turn off your camera, anything touching the shutter button may turn it on and run your battery down, even a strong bounce might turn it on repeatedly.
Get some good foam lining for your bike bag, 3/4 inch memory foam is a good shock absorber. or use some of the partitions out of old camera bags, I'm sure you are doing something like this now, don't just put them in a thin cloth pouch