I half-dropped my 7D and 100-400 and just grabbed it before they hit the ground but the lens hit the side of a coffee table and chipped a bit off the part where the IS, AF etc is adjusted leaving a hole.
I now find that when I sent in my 7D with a recently bought used 28-300 (which I wasn't convinced was working properly), the 7D had also suffered damage then - to the mirror box - at a cost of £250.
Also, the 28-300 has a faulty AF motor (another £250) but as its still in its 3 month warranty, I am talking to the shop I got it from. If they will pay for the repair, I will keep the lens.
So, not too happy at moment.