Well I remembered where I first read about using the Lumix OVF on the GR, and it was here on Colin Steel's site
http://phototravelasia.blogspot.sg/ in the post from September. You may have noticed that a more recent post about the GR is up, and it's currently featured on Stevehuffphoto.com
http://www.stevehuffphoto.com/2013/11/23/the-ricoh-gr-tokyo-style-by-colin-steel/
I received mine a little while ago. I can confirm that it works great as far as the FOV goes. The frame lines correspond to a final image that's just a hair bigger. The frame is off for the wide angle lens, as I should have suspected, plus you see the lens itself in the bottom quarter of the frame.
The back of the viewfinder only sticks out a few mm from the rear of the camera, so I find it kind of hard to get a comfortable position for my eye. I finally found that with my nose and mouth clear of the lcd and off to the left side of the camera (I'm right eye'd) I can tilt my head in an only slightly ridiculous fashion to get a good position for my eyeball. I wear glasses, and my thinner wire frames work better than the thicker plastic ones, but I suppose that's always the case. But either way the lenses of my glasses are forced right up against the rigid plastic of the vf, and that can't be good. (For now I've put on a few tiny strips of gaffer's tape to smooth the hard edges a bit.)
In general, I've never been all that invested in using a vf as far as framing the image goes. I like using the lcd. I have no problem with cropping, and enjoy having decisions made in front of the computer be a part of the process. So I'm not exactly traditional. But I've found that when I was shooting from the hip in free-flowing situations, I was ending up with basically garbage most of the time. So maybe using a VF can instill some discipline and I'll have less and crazy canted angles and less mostly empty frames with only a part of a person hanging off the trailing edge. Extra stability is always good, though the GR is not crying out for it, and if I had to choose I'd rather get stability via a tilting LCD that you can hold against the body. But I'm really liking using the Lumix for now, plus it's tiny.
*Edit* to update that, 24 hours later, I'm now pretty enthusiastic about this combo. I spent a couple hours walking around the city today with the slanting late Autumn sun pretty much at my back, and into my camera, for good chunks of time. The Lumix OVF performed like a champ - perfectly clear viewfinder in a situation that would seriously cripple any EVF or LCD, in my experience. I'm beginning to see the beauty of it. Plus something I never thought about - you can use your polarized sunglasses no problem. I get serious interference when I attempt that with my Olympus vf4