Changing the ISO on the EOS 40D just requires pushing a dedicated button then spinning the top wheel. You can see the ISO displayed on the top LCD, on the rear screen and in the viewfinder. No menus are required.
The problem isn't that there is no quick access to the ISO (pressing the ISO button on my GF1 also allows me to scroll thru ISO values with the wheel). It's that when you're changing ISOs, the camera does not update its exposure reading until you're done. The Canon behaves the same way - I just tested this with the EOS 40D as well. While you can change ISOs with the main wheel (once you have the ISO button depressed), you do not get a real-time exposure update as you would by changing aperture or shutter speed. The EV needle will move with the latter two, but when you change ISO, it won't update until you half-press the shutter to take a new exposure reading.
This tells me that the paradigm is still working on the assumption that ISO is a fixed quantity while shutter speed and aperture are your controlling variables, which is what I'm saying needs updating with today's digital sensors. Then again, I hear that Canon's intermediate ISO steps are push/pulls of the 'base' ISO steps, so maybe Canon is quietly trying to get you to stick to the base ISO?
@ Titan. Sometimes, the 'proper' way to take a shot is to expose incorrectly, then PP. For instance, I might underexpose a bright scene to preserve highlight detail, then adjust the curves/exposure in PP. If one were to expose "correctly", that might mean blowing out the highlights and losing the information there. It was the same in my film days, when I would expose to get the most information I could in the scene (I'd like to be able to say I used the Zone System, but in reality I was always too impatient and usually just guessed
), then run a set of timing prints and burn/dodge as necessary in the print. I also don't always trust the camera's exposure meter, or even histogram, but experience with the camera has let me anticipate how it behaves (for example, my GF1 likes to overexpose in bright scenes and underexpose dark ones - ridiculous, I know - so I can fix that by dialing in +/- 2/3 EV as needed). Although I'm quite impressed that the latitude of digital sensors is approaching (and in some ways exceeding) that of film these days.
Wind, Sand and Stars.