I went for a walk in the woods yesterday with the 5D Mark II and my 28-135mm IS lens. It was a gray day, and all the plants are stripped bare now, so it wasn't the most colorful trip. I decided to shoot jpeg instead of RAW because the files are much more manageable — RAW files are 20-25MB, vs. 6-12MB for the jpegs. I have an older computer, so the RAW files really gum up the works.
The little stream near where I live.
I've always felt Canon threw a useless battery meter into the cameras I've had: it tells you that it's full, or that it's about to run out. The 5D Mark II has a nice battery meter. The icon you see in the viewfinder now has 4 different levels, so there's not so much guesswork involved.
There's also a "battery check" function, but it's buried in a menu somewhere. No problem, I just assigned it to "My Menu" for easy access. It tells you remaining capacity (in a percentage), shutter count (for the current battery charge — this is reset upon removal of the battery), and has a 3-bar "recharge performance" meter which indicates the overall health of the battery.
I walked around for 2.5 hours in 35-degree weather yesterday, and the battery's sitting at 84% today. I was doing a lot of chimping as I went, played around with live view a bit, too. I've never had an issue with battery performance with any Canon DLSR I've had.
The 5D Mark II uses a new battery, so the BP-511 and BP-511A batteries are incompatible.
The reason you want a camera with a full-frame sensor is so you can shoot wide. The widest EF lenses I have are 28mm — which is a normal field of view on APS-C sensor cameras like the 40D. But on the 5D Mark II, they're moderate wide-angle lenses. Nice! I really like 28mm as a walk-around focal length.
One thing I do miss from the 40D, however, is its fast burst mode. I encountered numerous deer on my walk, and would have liked to been able to shoot faster. The 5D Mark II's burst feels like the slow burst on the 40D (or, for that matter, the 300D). It's understandable, given the sheer volume of information accumulated with each shot.
I failed to photograph a deer, but I don't blame the camera for that. I just like how fast the 40D can shoot.
Foam swirling in the stream