About a week ago I took delivery of a Fuji GA645Zi, and started learning how to use it. I found that there is a bit of a learning curve, but nowhere near what I am used to on my DSLRs. The main thing I didn't like was that it doesn't have a separate shutter-speed dial. For my trip to Hawaii I really like how compact it is, as well as being very light. In fact it is somewhat smaller and lighter than my Nikon D3.
However, I did want to try the 670 because it is 100% mechanical. I received the GW670 a few hours ago, and it's going back to KEH. Not because it is a bad camera. The camera is simplicity itself to use. More so than the GA645Zi. I found the rangefinder focusing quite easy to use. Since I will be shooting mostly landscapes it would probably stay set on infinity. However, for my trip to Hawaii it is too bulky. The other thing is that on a 120 roll of film you only get 10 exposures compared to 16. Granted the 670 negs are a lot bigger, but I'm not planning on making huge prints. I also like the zoom feature on the Zi which gives a wider field of view than the 670. The main downside to the Zi is the slow lens especially at the long end. I don't see that as real problem because I'm not going to be using it for action shots. This is going to be primarily a landscape camera.