I bought one last year as a replacement for a Sony DSC-P200, which I hate. The feature set is fab, raw is a big plus and I thought 580EX compatibility was nifty too. It is a little on the large side, for a "compoact", but I knew that and figured the technical spec and manual and Av/TV controls and quick EC were well worth the bulge in my trousers. That's what I thought inititally, before using it in practice.
In practice I found the usage of the thing to be an awful experience. That's not the fault of the G10 at all, but simply the reality of P&S cameras vs DSLRs. The thing has a viewfinder. For stability I want to shoot with the viewfinder, and not hold the thing at arm's length. But there is no information in the viewfinder at all. So to set the thing up you need to use the LCD screen, then turn the screen off, put the camera to your eye for the shot, and then turn on the screen again to see if you got what you wanted. Any adjustments need the screen again and it's all a bit of a faff. Furthermore, I am using manual exposure increasingly - probably 90% of the time, if not more, with my DSLRs. A Zoom lens with a variable max aperture is about as appealing as a pin in the eye, if you want to shoot with manual exposure. You can't just set things up for the ambient light conditions and freely zoom in and out. You have to zoom/compose first, then set up your exposure, turn off the screen, put the camera to your eye etc. etc..
I concluded that I would end up using the G10 as a basic point and shoot and the extra features would be a complete waste and an expensive one at that. Also, a 580EX on top of a G10 is quite frankly ludicrous. You end up with a huge, top heavy package, and might as well just use a DSLR in the first place.
So my G10 went back for a refund (Jessops 30 day return deal) and I bought a refurb Fuji F100fd instead. Since the G10 cost me around £335 and the Fuji was £112 it seemed a better use of my money. FWIW I hate the Fuji, and almost wish I'd kept the G10, but in truth I just hate compact cameras altogether and having the G10 was just a bit silly.
My philosophy is really that if I want to do photography then I want a DSLR to do it with. If the occasion does not warrant a DSLR then, from my perspective, there's really no need to take a camera at all. Of course, I don't have a family, so snapshot style memories are not something I feel compelled to want. For others it may be very different. But if it's snapshots you're after the G10 perhaps does not offer the best value for money, or the most pocketable convenience.
I've had the Fuji for 6 months and only have five shots I've bothered keeping during all that time. To be honest they could probably binned as well.
I don't know how many DSLRs you have but I would hang on to the 30D as a backup body or to serve your wide angle needs while the long lens is on the 40D. I spent three weeks touring New Zealand a while back and had a 30D with 10-22 and 40D with 100-400 and took them with me everywhere I went. No need for lens changing, Always had a backup body with me. No issues with dust or dropping things. When I started shooting weddings I had my 17-55 on the 30D and 70-200 on the 40D. I've now upgraded my kit (1D3 and 50D) but two cameras is always a sweet setup whenever I need two lenses on the go at the same time. The Fuji rarely leaves home.
All IMHO
p.s. I never had a problem with the IQ from the G10, given the crazy pixel count on that tiddly sensor, but it was the operational ergonomics that made it poor value for me.
