I have seen Carbon go through a "catastrophic failure" once, right in front of me. A Cannondale super 6 evo, while my buddy was standing to climb. He's built like a sprinter, and rides hard. The non-drive seat stay snapped in two, about 5 cm above the drop-out. Made a very loud noise. Cannondale sent him a new frame, which he sold. He's on a Venge now.
I personally cracked an aluminum frame, near the BB.
I've never hurt steel (both main bikes are Italian steel now), nor have I seen it damaged except by crashing into things (which will damage anything).
My trepidation on carbon is not based on a fear of it somehow being more prone to breakage while riding. I just don't think it is, and I'd say 90% of my riding buds are on carbon. It's based on two things: first, it can break in a big way when it does, which could contribute to harm to me (not likely, and wouldn't stop me from getting one); second, it is known to be weakened by stuff that happens to bikes (like the kid knocking it over, or the fork being dinged, etc.) because it is designed for great strength in one vector (where the forces are applied whine riding) but not necessarily in another.
If (and maybe when) I own a carbon bike, I will be much more careful with it, and I treat my steel rides very well.