The quietest camera I own is the Ricoh GR-D. The Epson R-D1 is noisier, but not noisy enough to ever be a problem, and I do a lot of close-quarters street photography with it. I think the number of photographers for whom a deadly quiet shutter is a frequent necessity must be very small indeed, although it seems to get no end of discussion on internet forums for some reason. FWIW my DSLR is a Canon 300D, and the shutter on that is pretty quiet too.
Ian