Extreme use...do not try this, at home or elsewhere...
I've used the 7D now for going on two years, and it has performed spectacularly, with two exceptions. First the good news: no focus issues, great firing rate, clean images with fast glass (I own mostly fixed f2.8 lenses, zoom and fixed). I recently picked up the Canon 15-85mm zoom and it also performs very well on the 7D and vice-versa, and therefore has become my walk-around setup. Yes, I gave up some f-stop but the range is perfect for any of my personal, non-pro shooting.
Recently stressed the 7D in two situations, both very wet. First, went to Niagara Falls and traveled out on the Maid of the Mist boat to the foot of the Horseshoe falls, tons of watter falling out of the air around me. I shot with the 7D and the Canon 15-85 lens until the water collecting on the front of the lens filter started to blur the view, at that point autofocus completely failed (as might be expected), which prevented any shots, but otherwise camera was fine.
Second, hiked the Watkins Glen Gorge amid waterfalls throwing plenty of water around and was careful to protect the 7D and keep wiping the lens filter clean but some moisture must have gotten into the camera body because it went berserk. First an error msg appeared that said the camera could not fire, and telling me to stop/start the camera and possibly reload the battery. Then, even with the power off, the shutter fired nonstop for 2 secs until I could pull the battery. No damage to the storage card, none to the camera as I dried everything with a clean, dry handkerchief, reloaded the battery and then the 7D worked fine.
BTW I was never "under water" or being deluged in either situation, just lightly sprayed here and there and protected the camera with my body and rain jacket. So for those of you who shoot in high moisture situations, be aware that this camera needs protection, and the lens has to be clear and unblurred in order for the camera focus to work and allow you to release the shutter.