I have discussed this with some of my peers, and while the backs seem to produce exemplary image quality, many photographers look at photos as reproduced at point-of-purchase displays, magazines, etc., etc and can not tell which camera was used to shoot what image. For example I just shot something for point-of-purchase for Bergdorf Goodman, Neimans, etc. on a 1Ds3 and it will sit right next to other advertising which was shot with 4x5 film, 39mp back, etc. And photographers go stick their noses up to the prints and can not tell what camera shot what - so why invest in the large clunky expensive stuff? I agree that the shape of 67 or 645 is nicer than 35mm, it feels good to shoot, etc. but when the client nor the consumer can percieve any advantage in terms of end-result IQ, and the economy in the sh*tter, then...no sale! Even on a reasonably priced lightly used back. I mean, I hear this time and time again from other photographers - about the lack of visible difference in the final reproduction, and I usually feel the same myself. (I have owned and rented Leaf, etc., etc.) Clients have not asked me for more pixels or higher IQ in YEARS. And I have shot for some very high end, high budget clients. I think just about the only time most of us can see which camera was used is when someone like Paolo Roversi has been shooting polaroid, or someone is using tilts with their view camera...otherwise, open up a magazine and tell me which camera shot what...for the most part, it's impossible as far as I can tell.
if you shoot with a lot of light (usually flash), or slower setups, more static imagery with a lot of post production manipulation medium format has it's place.
anything past that, continuous light, especially low or challanged light, fast moving subjects, quick changes and setups then I agree a 1ds3 is probably going to out perform nearly any medium format back. on my desk are two covers, one from harpers and the other from vanity fare and I know one was shot with a canon I assume the other also, given the photographer's history.
they both look fine, they both are printed reasonably well and the photographs and the photographers are well respected. shooting them with anything beyond a dslr would have been a waste of time and money.
right now, regardless of the new mf price reductions I believe the medium format still camera business is in for a tough ride.
the companies have been slow to respond to their customers main requests, the prices, even reduced are high and most importantly in this economy clients are demanding twice the output in 1/2 the time. this holds true for high profile and under the radar clients.
I also like the feel of a medium format camera and when shot properly it's a pleasure to use, but for commerce, even editorial in today's business climate we have to perform at a very fast pace and the dslrs are made for that.
we just finished a studio shoot that was perfect for medium format, but still just went with the canons. bottom line it was easier and faster, for me and for the client.
I own mf camera backs and don't see the point of selling them at a reduced, bargain basement rate, but it would take a very special project of circumstance for me to upgrade my backs to higher priced options and as lisa r says, nobody is asking for more file size.
clients are asking for more return on their investment. as photographers we have to do the same.