I've been bitten hard by that bug as well, and also there seems to be a TLR bug going around and it has similarly infected me. I was using an old Rolleiflex with a Tessar 3.5 but just the other day acquired a Mamiya C220 that was being used as a bookend - in great condition, protected by a soft case and all that - with an 80mm lens. I finally took it out for a test run and I have to say I was blown away by the results! Those Mamiya lenses, even for the TLR, are quite sharp and contrasty, and based upon that it will become one of my most used cameras.
Yes, it is heavier/bulkier than the Rollei, but not really by that much and I would not hesitate to take in on a tough uphill hike to get a shot. And as soon as I can afford to I want to get some more lenses for it (another plus over the fixed lens cameras). There are some Mamiya user groups (at the Mamiya web site for one) as well as a TLR message board I found once but haven't been able to find again that absolutely rave about the wider angle lenses - which of course go for much bigger bucks on the auction sites.
In summation, based on what I have learned 'in the field' and on my preferred subject matter (portraits), if I were just getting into it today I would only be interested in the Mamiya. You'll have to decide what works for you and your subject matter, but as far as results I can highly recommend the Mamiya as giving the most bang for the buck - especially since very well cared for Mamiyas with 80mm lenses are going for under - sometimes well under - $200 on the auction sites.