I am a canon film SLR and DSLR users for quite some years. I have not used either of them but based on paper information the specifications of the two cameras are quite different in the range of the zoom lens and the CCD they use. In theory the G7 should produce better quality images but I am not sure in practice they are that different. The S5is however has a 12X optical zoom lens so if u like shoot in long (really long - u would need a tripod in theory?) telephoto this is an advantage. However, given the low price of 400D personally I would highly recommend buying a 400D instead of any of the two cameras you are looking at. I did like the G series camera a lot in the past but I do not like the fact that they take away the option of shooting RAW in moving grom G6 to G7. For me if I have to choose one I would get a G7 as I seldom shoot in longer than 135mm.
