I decided to really put my micro 4/3 GFI to the test yesterday and get some indoor shots of the kids. Frankly, I was a bit surprised. While the 20mm f/1.7 does very well in low light - it is 3 stops faster than the 45-200mm zoom. As soon as I started trying to work with the telephoto the AF was not great and the viewfinder was sluggish, even with relatively bright room lights.
My 40D, even with the f/4 zoom, was snappy and spot on for focus. This is pretty much a deal breaker - micro 4/3 is perfect for stock photography where I tend to have time and bright light. Small, easy to carry and cheaper, and I will continue to use it for that. But for now I'm just going to stick with what I have. Might as well try to learn to push the envelope on my current gear.
Flash was the other deal breaker - a big bounce flash is just huge on my GF1. If I switch to the Panasonic flash it would be easier to use, but then I lose all the nice wireless feature of my Canon system.