I once did a spectacularly wonderful involuntary dismount from my mountain bike though ... I was bombing down some singletrack which suddenly became deeply rutted. My wheels became trapped in the rut and I was not able to slow down enough before the rut came to an end. The front wheel dug in and launched me over the bars. My shoes unclipped themselves from the pedals and I cleared the handlebars, landed on my feet and was able to keep my balance by running away from the fallen bike!