My last crash happened when I unexpectedly came upon a huge diesel spill covering the road in the middle of a turn. Went down so fast, I never even got my hands off the bars. I was wearing my helmet at the time and good thing, too, because... oh wait, it never impacted anything. I landed on my shoulder and my face (jaw) and went sliding down the street in a pool of diesel. Almost knocked me out and I had a headache for 3 days, but my helmet, unscathed, lived to ride another day!
From the fun with statistics department: All the people I *personally* knew who died as a result of collision or crash while riding their bicycle (sample size: 3), all of them were wearing helmets. So, 100% mortality rate!
Also, I love it when someone says after a crash while showing me a cracked helmet, "the helmet saved my life!" I usually respond with, "how do you know that? Have you previously had a similar crash for comparison purposes and not survived?"
Now of course, I believe that a bike helmet has some protective capacities. I just believe risk of riding without one has been overstated, especially for people with decent bike handling skills