[NB Accident was completely self inflicted on a forest track]
I was out for quite bit, woke up cold and with trousers shredded on left side. Was in a lot of pain for a couple of days and ended up with a spectacular giant hematoma on my left hip.
My first reaction on coming round after being knocked out was, of course, "I hope nobody saw that" :-)
Edit: I kept the helmet (or remains of the helmet) for years to show other people.
Otherwise basically the same for me (I'm told) - bike slammed over onto the right, walloped me into the road, and then skidded along the ground with me still attached and out cold. Knee and right shoulder blade were skinned but that was it.
You mean you can't use your legs to save you because they're attached to your pedals? That sounds incredibly dangerous.
NB The accident was completely my own fault (tired, went cycling after a 250 mile drive, getting dark, out alone...)
Most helmets now have a plastic skin over the foam which provides some structural integrity while the foam is being crushed [1]. But you are correct, the helmet only works because the kinetic energy is being absorbed by a material whose composition (closed cells) will naturally break apart into smaller pieces when enough kinetic energy is applied.
[1] http://www.bhsi.org/general.htm