Tim,
My background of cameras and lenses leads me to want longer zoom reach than that of the G10, or that offered by other brands. However, I don't want the camera size of the Canon SX10 (or the new SX20). The SX10 has the 20x zoom range of 28 - 560mm equivalent. The G9 has 6x of 35 - 210mm, and the 2x tele conversion lens takes that out to 420mm equivalent.
My old film SLR was a Nikon FTn, with three lenses; 28mm, 50mm, and 135mm. I used to think that was adequate, but often wanted more reach, but not another lens.
My first digi-cam was a Kodak DC4800 with a 3x zoom of 28 -84mm. It was nice, but the reach was too short. I also used a Kodak tele conversion lens with it, but the quality was not good. My next was the Canon A620 with 4x zoom of 35 - 140mm, still too short. I did not get any conversion lenses for it. Then I moved to the G9 taking me out to 210mm. This works for me most of the time, but when I want more, I use the 2x converter.
I can also use the built-in 2x Digital Tele-Converter (or the 1.5x), and take a must-have shot, but the quality is not as good as using the tele conversion lens. I can also take the shot at full 6x optical (12MP) and crop at home, with fairly good results, but not as good as using the lens. If I am at maximum zoom with the doubler, then I will get a better, sharper image if I also use a tripod. The image stabilization can do only so much.
Dennis