1. In terms of image quality, how does the G9 compare against the D40 with kit lens?
Two issues to consider: Iso and metering.
1. ISO: at high ISO, the G9 - and 99.9% of compact cameras - will be not very good past 400 ISO, maybe 800 is you don't enlarge your pictures past postcard-size. The D40 - and most digital SLRs - will be better in that regard due to the inherent advantage of the larger sensor. HOWEVER, I have taken pictures with my G9 at 1600 ISO that have turned out quite good, in my opinion comparable to what the D40 would do. BUT, it required using a noise-cleaning software such as Noise Ninja (which I use). So you can get good high ISO results with the G9, but you have to "bend the rules" a little, so to speak...Mind you, this caveat would then apply to any other compact camera.
2. Metering: is the metering on the G9 any good, or comparable to the D40? I haven't done any scientific testing, but it's very, very good. The G9 is a fully-featured camera that allows you a lot of manual control, including centre-weighted metering. I would say that you could get very close metering results to the D40 by using the G9, but it would take you slightly longer, because it's a bit more fiddly than a larger-bodied camera.
2. How noticeable is the difference in size between these cameras when held in hand in real life?
Wrong question, my friend!...
Of course there will be a size difference, with the D40 being bigger. But, the D40 is much more ergonomic, because the G9 is...well...like a brick. it's part of its charm, because it's "old school-style", but there are no edges to hold on to. So, as far as "handle-ability" the G9 IS smaller, but feels more awkward to handle. I would go as far as saying that in a hot day, you might want to use a strap, because that little sucker - metal-bodied as it is - would get more slippery than a greased body in a Turkish bath house! In short, the D40 is bigger, but feels better in the hands. Still, I love the G9!
3. Are wideangle lens convertors available for the G9, and how good are they really?
Yes, there are available: http://www.lensmateonline.com/newsite/G7.html
Better than what Canon makes, I think - see for yourself in the examples on the website. You can get zoom extenders, wide-angle converters, Infra Red...Check it out. How good are they?...Ok for postcard-size, I reckon, but it won't match the image quality you could get with, say the D40. However, lenses (wide-angle, zoom, etc) for D40 will be more expensive than these G9 converters. In short, are they "a solution"? I don't think so, honestly...It's a
solution, yes, but you loose the small-size factor because of the adaptors, and with the adaptors you don't get SLR-quality pictures either - a bit of no-man's land... Or is that a "niche" market?...