I'm on my THIRD camera bag since purchasing my G. My original criteria was just 'small and unobtrusive', so I originally had one of the Benetton shoulder bags, a very small unit. It proved to be too small (first bitch) and not so comfortable for me. The nicest feature was the top zip. So, my second bag was a LowePro Adventure 2 (rucksack style). A very small bag. But again, just a little too small.
I modified my criteria slightly after travelling a bit with the G2. I needed 'small, unobtrusive, wearable on the shoulder or crosswise, to take sideways strain off my back, and a little extra space for a map or two, perhaps a paperback.
I finally settled (after tearing apart the camera luggage sections in 2 or 3 different shops here in Tokyo) on one that for me, is perfect, and is also a pretty good fit for the G system. The LowePro Linx 220. It gives you access to your lenses etc through a top zip, but in addition, you can pull your camera directly out of the side through a small side zip (assuming you have a short lens mounted - that trick doesn't work with the 90mm). Plenty of small inside pockets, and some nice features lacking in the other bags I had - a rear outside sleeve (perfect for a couple of maps and a paperback book when travelling!) and a nice array of other pockets plus a small padded velcroed shelf between your camera and the top-most zipper. Nice, compact protection.
And comfortable to carry, since the carry strap is thick, well-padded, and this can be carried very comfortably on the shoulder, or cross-wise messenger-bag style. It really seems like a well-modified messenger bag, and doesn't really look like a camera bag (nice feature). The strap is thick enough that there is NO WAY someone could run by you and slice through it to steal your bag. They would have to perhaps be carrying a japanese katana to do so.
Hope this helps. I've had plenty of frustration with bags that were uncomfortable or just too small, or just too inconvenient; on some occasions, I even wrapped my G in one of those padded velcro wraps and dropped it in my regular backpack, the other two camera bags were more of a pain than anything else.