I've had a G7 and played with my son-in-law's G9, and also have an M8. I agree with everything Nick said; the G9's a brilliant piece of work. But the Leica's image quality is better. It's not as small, but you can easily carry it just as Nick said he carried the G9, with a handstrap. You can stick a 21 on the camera, carry a 35 and a 90 in your pockets; or, if it's bright, a WATE and the standard TE, plus a 75 or 90.
Pocket-fitting or not-pocket-fitting seems to me to be the critical point; if I were willing to take a along a camera that it didn't fit in my pocket, might as well shoot the Leica. If I decided I needed or wanted to a camera in my pocket, I'd have made up my mind in advance that I'd be giving up picture quality. (Which is usually fine with me; I'm not usually traveling to take photos.)
When I travel to travel, I currently carry a Leica D-Lux 3, which I stupidly bought for fashion reasons, and is not nearly as good a camera as the G9; it is, however, more expensive. 8-) The D-Lux does have a better lens, I think. My dream camera of this sort would be a Fuji sensor of ~8-10mp in a G9 with a Leica zoom. All the parts are there, just not from the same people.
One thing that most people don't talk about, concerning the Leica, is that if you take along an assortment of lenses (a WATE, and fast 21, 35, 50, 75, 135), that means, for me at least, that I'm often leaving $10,000+ in lenses in a hotel room. I do it, but I'm always relieved to get back and find them still there...
JC