I've got a 7D and it can produce some jaw dropping images, however it is not like picking up a camcorder and going off to film with it. You really need to set up each shot and have a high degree of control of your subject. In my opinion it's more suitable to studio type work where everything is storyboarded and you know exactly what shots you need, rather than natural history work where you may not even know what story you'll come across that day. Those are general rules, but nothing is impossible of course.
I've used the 7D for the last two weeks as a complimentary camera to my V1 for topside shooting. In that capacity it worked fantastically and produced some images that knocked the spots off those ones captured by the V1. Would I have been happy without taking the V1 and just taking the 7D? Absolutely no way and if I had to choose one camera to take I'd have taken the V1.
Two working examples. Example A: Hermit crabs fighting over a new shell on the beach. The 7D performed superbly. With a 100mm EF macro lens the images were outstanding. The subjects didn't move very far, I was able to set up the shots (although not easily) and get the images I wanted. Example B: Juvenile Sharks swimming in a shallow lagoon filmed from the surface while wading in the water. The 7D just wouldn't cut it, using a combination of the 100mm EF lens above, a 55-200mm EF IS zoom lens and a 17-55mm zoom lens. There was constant movements and changes in the distance of the subjects. I had to go back to shore to keep changing lenses to try different approaches. With the CMOS jello effect (massive problem on the 7D compared to a camcorder with a CMOS sensor) and the shallow DOF of some of the lenses I was using it was impossible to get the shots I needed even after trying for a couple of hours. I do have a 70-400mm telephoto lens, but didn't have that with me at the time and can't image in would have been practical to use. I eventually changed cameras to the V1 and got all the shots I needed within 5 minutes.
Hope this helps.
