I've fallen once while clipped in on my road bike. End of the ride, unclipped my left foot and didnt watch where my wheel was going, so the bike tilted towards the right and I fell down. This was with SPD-SLs. This was about 2 months after I had gone clipless.
Late August, on a downhill run, I hit a sandy patch that I wasnt expecting, my front wheel got stuck and twisted to the side, launching me off the bike. Without thinking, i managed to get both feet unclipped, clear the handlebars and landed on my feet. Even the Russian judge would have given me a 10 for that. This was with Speedplay Frogs.
I agree with UMD's broader picture comment that really, it isnt that hard to ride clipless. But most clipless riders I have spoken to have fallen atleast once. I dont think I personally know anyone who has -never- fallen, actually.
V.