I was riding the "express" tour d'ile today. I started a group that wound up snowballing into the 2nd group on the ride with about 75 people in it. I noticed right away that there were some clowns in it. I personally don't have much close quarters riding experience but I just err on the side of being safe. I nearly got wiped out a couple times by people cutting me off. Anyway, we came to a hill where it narrowed (because we used one side of a dual carriageway) and some guys were just all over the place, passing far to close to each other, weaving all over the place. Then it happened, somebody near the front when down (with a look of horror on his face). I'd say about 10 people went down, including myself. However, I could not return to finish the remaining 2 miles.
I have, 2 finished tubes, 2 wheels out of true (1 so much that I can't even release the brakes to make it move freely), 1 finished tire (both tires were nearing the end of their lifespan anyway), 1 wrecked waterbottle cage (possibly 2) and some hurt pride.
Luckily I went down on my left so my deraillers are unscathed.