I am in the Maldives and stole my wife's G9 that she was not using. I have to say as an experienced DSLR photographer I was amazed at this camera. I had bought the Canon underwater housing and figured it would be OK to risk this camera underwater. With the G9 I really did not miss my 40D or 5DII that much. Sure there are some situations where I would have had more flexibility, but it really is amazing what this little camera is capable off.
The things I wish could be improved are the following:
1. The camera is very difficult to control underwater when using RAW. It is extremely hard to free dive and then find your prey that you want to shoot and then juggle 2 buttons at the same time trying to get the correct exposure. Obviously the light at 60 feet is different than 12 feet and you need something very quick to adjust the lighting. And if you want to shoot RAW (in order to be able to have full WB control) you need to press 2 buttons at the same time and juggle a third to get a good exposure.
2. Better high ISO images. The P&S capability of the G9 is obvious in this case. Anything above 400 ISO is not very good. I would guess that ISO 1600 or even 3200 on the 5DII would be equivalent to ISO 400 or 800 on the G9. High ISO is very very useful for underwater pictures as it allows you to use a fast shutter speed with little light. I read that the G11 has 2 stop advantage over the G9, if so that is a HUGE improvement.
3. Tilt viewer not available. Again this seems to have been fixed in the G11. I found myself on many cases wishing I could pivot the viewer for a better angle on a picture. This will be a great advantage on many types of pictures.
4. The largest aperature is 8.0 While that seems to get excellent pictures and has good depth of field, I found that in many cases I have to push the shutter speed above 1000 ... which seems like a waste of possible aperature flexibility. Not sure what the G11 has but if this would be say f16 this would be fantastic.
5. Flash is not very strong. It is hard to criticize that as this is a P&S camera and even some DSLR's don't even have a flash. It is a good idea to get one of Canon's small slave flashes as an add on if you plan a trip. Flash is ofcourse very useful at night and even more so if taking pictures with a lot of light where a face is superimposed with a picture. You need something strong that can go through the dark shadows that human faces inevitably have when put on high contrast landscape.
6. There is no optical zoom on video. There is digital zoom but that is not an option I am interested in. I think they left it out because of internal noise of mechanical movement of the lens. I think they should keep it on as in many cases audio is dubbed with something else and thus mechanical noise will not be a factor. Otherwise the video is quite good, just make sure you have high resolution on and not the video with the little envelope on (something I did

). This cost me a full day free diving and as you can imagine, that was the day I saw and videoed a large shark, a large turtle and a huge grouper.
I might put some pictures and make a full review with the G9. I think the G9 and G10 and G11 are very similar so this could be useful to someone who is planning on such a camera. But really this little camera packs a tremendous punch and I for one am absolutely going to jump on the G11.