Cindy, Maggie, Carl -- wow, thanks for the encouragement!
Cindy, the Hassy and Mamiya are really 2 different animals. The Hassy is unlike any camera that I have used, and honestly that is a large part of its appeal. Square format, big, heavy, loud shutter, but also brilliantly engineered. Focusing is fast and easy, and I love the 150mm Zeiss Sonnar, it really fits with what I have been shooting lately. Handheld shooting is not a problem. I normally just carry a camera with a wrist strap and put a few rolls of film in my pocket. The Hassy is too big for that, so I have shoulder strap on it, but the size doesn't really bother me.
As you know better than most, the Mamiya is very portable, and unbelievably quiet. Very much like a large Leica M. Easier to shoot handheld than the Hassy, especially at slower shutter speeds. I am slightly burned out on rangefinders, so the Hassy is getting more use at the moment, but I plan to use the 7 more frequently soon.