Hi, I have had a 600D for about two months and after having the 40D my back has recovered from the dreaded pain due to the light weight and the fantastic articulating screen; good for being able to take low shots and with live view being able to focus acurately, therefore macro shots become easier. The controls on the back are all together and easy to use the "Q" button especially. The end results are better than my 40D (slightly) and I am very pleased with it so far. The video capture is good but I am only just starting on this so still have to learn the ins and outs. Possible downside could be weight ratio using long heavy lenses but it is what you get used to. If you where to purchase one then get an extra battery as live veiw knocks hell out of it and I find using liveview and macro drains the battery, in normal useage the battery seems to last a simmilar time as my 40D allso I leave the quick release bracket fixing of my tripod on the camera and this does not allow me to change the battery without releasing the bracket, little thing but annoying.
There are a number of features on the camera which I have to explore but in time I hope to learn more. Hope this helps. Well pleased with the 600D.
Good luck.
David