Humm, just got my Mamiya 645 and reading all this. I admit I was thinking it would largely supplant both my Yashicamat and, once I had a few lenses, my 35mm, but I think it's too large to do either. The Yashica is far handier to carry around even including the light meter I have to carry (and my Luna Pro SBC is not a small meter) and likewise it's too big to fully replace the 35mm gear. But I'm still thinking I'll like it for the combination of interchangeable lenses, some automation (AE prims finder and winder grip) and medium format with interchangeable backs.