Well, first time I've ever used my helmet (as opposed to wearing it) was yesterday.
Light rain, tram tracks, a last-minute decision to make a turn - made it fine across the first track - front wheel slides straight out on the second one. Bam! Palm of glove gone, noggin bounced off the road, elbow and knee slightly redder than they've been for a while.
I've had falls before, but this is the first time I've felt my head bounce off the road. Able to get straight up and off the road, fortunately, and ride away after a few minutes of minor repairs to me and the bike.