I bought this pouch for my Canon G11 and I am very please with it. There is enough space for the camera, a spare battery, cloth and spare memory card. I could probably get in some more slim items, but that's all I need. The pouch is divided into two compartments - one that fits the camera proper (with just enough space for the neck strap) and the front compartment which can hold a spare battery and other accessories.
There are two options of carrying the pouch - a clip on neck strap which is provided (which make it look a little like a ladies handbag, so your mileage may vary with that option). The second option is a high quality and robust belt attachment that actually has a Velcro arrangement that means you don't have to undo your belt to thread it through.
Even though I suspect the pouch is water resistant as it is, I quite liked the pull out "all weather cover" that can cover the entire pouch and protect it from rain while it is attached to your belt - somewhat like the rain covers you see on high-end backpacks. It pulls out from the rear bottom, and reaches around the bottom, up the front and over the top, so only the part facing your body would not be covered.
The pouch feels very robust, and suits my "outdoor" mentality - I feel quite comfortable bringing my camera on hikes in all kinds of weather.
My only complaint is the space for the G11 neck strap - it fits if you fold the strap neatly and pack it in carefully. I think I may end up downgrading the neck strap for a smaller wrist strap (I don't want to be completely strapless as I don;t trust myself not to drop my camera!). That would then leave a bit more space for other items.
I doubt you could fit a flash into the pouch - but if you have loads of equipment, then really you probably should be looking at a larger case altogether.
I add a silica gel packet to the inside to keep the inside dry.