I had been playing around with the ISO settings. As so far I have just two lenses, 50mm 1.8 and kit lens (18-55). So far my view agrees with rest of the people who are using this wonderful piece of equipment. A 20D body and 50mm Lens combo is quite fun. It kind of make things interesting when I can not zoom in/out while standing at one place and actually needs to move around to make the right composition.
Anyways, about the high ISO, it seems that I can use upto ISO 800 without even thinking about it. ISO 1600 is acceptable and in most cases works well with a bit of post processing (which I am currently learning the ropes of). ISO 3200 is not something I have tried yet. Never needed it.
The best part is, this camera is easy to handhold. I have been able to handhold 1/8 sec exposure most of the time. Specially with continuous shooting mode. I take small bursts and one of the picture turns out to be good enough to be a keeper. With the vertical grip BG-E2, this camera size up real nice.
The following snapshot I took while taking a random walk.
ISO 100, F2, 1/50 sec, handheld
I did some color correction and levels changes in post processing using Photoshop Elements. Still even at full size this picture was quite acceptable.
One problem I saw while using Canon EF 50mm F1.8 is that strong lights will create some kind of reflection on the lens and will show up in the final picture. Apparently it happens when you are using a UV filter on the lens (which I am). I cloned out the light specs from the picture using elements while doing PP. Initially I was worried that this was due to some kind of dust particles on sensor or lens, but kind folks at http://www.uae-photo.com and canon 20D group on flickr reassured me that it was not so. I can not tell you how relieved I was.