Even though I raise (or support Bernard on) one quibble with Michael on the value status of the D3x, a camera that never ceases to amaze me in the thousand-plus high detail landscapes I have shot with it, I agree wholeheartedly with his fundamental point that image quality has gotten so good that camera manufacturers will have a much harder time selling us upgrades. The D3x actually supports that point, by replacing (much more expensive) low-end medium format for many applications. Every previous DSLR I have owned, I have had some issue with image quality - something (usually dynamic range) I wished was better. The D3x is good enough for me - I'll shoot this camera until the day the shutter dies. For photographers who don't print as big as 24x36, the "good enough" point is reached somewhere below the D3x, while exotic applications may demand yet more, while the basic point remains - "good enough" cameras are available now, where they weren't for a lot of purposes five years ago. A photographer who is lucky enough to shoot their own personal good enough camera can concentrate on learning their tool really well, on developing the relationship with their tool that Ansel had with his 8x10, or Henri Cartier-Bresson had with his Leica - knowing how their camera will "draw" (to use Sean Reid's term) each image. A few years ago, the question was was "how will each new generation of camera impact what I do" - now, for photographers whose work is well-matched to their camera, the question has become "how can I make this image with the tool I have chosen". An exciting day for photographers (although a sad one for camera company accountants). Hint to camera companies - photographers always want lenses, even when cameras are evolving more slowly!
We've reached a point where cameras HAVE become "good enough" for most purposes - the only difference I have with Michael is that I'd include the D3x as a part of that trend, rather than singling it out as an outlier away from the trend. The D3x offers the very best image quality available from small-format in a rugged body, without spending three times as much on medium format. Witness Phase's recent "who's afraid of the D3x" (my title, not theirs) promotion in which they give away FIVE lenses with purchase of a P45+. The D3x will make very, very good 24x36 inch prints - I'm still learning how, but my initial attempts are nothing to sneeze at, even as I learn the optimum sharpening and other adjustments for my combination of camera and printer (iPF6100). The dynamic range is just amazing (11 stops or so with texture, 9 with real detail - one stop on each end added to what the Zone System was designed for (Zone 0 is a textured black, not maximum black, and Zone X isn't paper white, but a textured white - real detail extends from Zone I to IX on the D3x) and the resolution is stunningly sharp. I will not claim that it can equal a P65+, because it can't, but comparisons against lower-end medium format digital are VERY close. It has added new print sizes to what I can do, up to 24x36. I don't know the Alpha well at all, but big prints I've seen from it are not D3x level (they're very good, but the D3x is substantially better).
When we can print 24x36 from carefully selected and used small format, where does that leave the state of photography today? We have access to an amazing range of cameras for every budget and need, and many of them are VERY reasonably priced. For hobbyist use and 8x10 printing, there are at least six manufacturers (Nikon, Canon, Sony, Panasonic, Olympus and Pentax) making great SLRs, any of which will deliver a superb 8x10 print. In this category, the camera I'm really looking forward to seeing is the little Micro 4/3 interchangeable lens "rangefinder" that Olympus has been showing under glass. The thing is the size of a G10 if not smaller, yet has an (arguably) SLR-size sensor in it and interchangeable Zuiko lenses. Oskar Barnack would have loved it, with its strong dose of Leica spirit. Some of the SLRs are under $400, and few if any in this category exceed $700.
In the advanced hobbyist/13x19 print category, there are 12 mp range DSLRs galore, many of them under $1000. You can get fully professional autofocus at the top of this category (from Nikon in the D300), a rotating screen on a few Sonys, compatibility with any lens line you choose, and even a full-frame camera (a clearance 5D mkI). All of them are under $1500, with only the D300 or a 5D pushing that figure (and both manufacturers have cheaper options).
In the category of cameras that match 17 inch printers well, there are still three manufacturers left, with a wide range of camera types and prices. There has not yet been a crop-frame SLR that has convinced me of its credentials at this level (will there ever be? - there are limits imposed by pixel size), but Canon, Nikon and Sony all make full-frame cameras that do. There's also a Canon reasonably priced on the used market (the 1Ds mkII) that certainly falls in this category. Perhaps the Alpha 900 or one of the newer Canons belongs even above this, intermediate between printer sizes (as Michael says, able to print 20x24). Cameras at this level are available below $2500, and there is a good choice of features - from 12 MP with a usable ISO 6400 to 21 MP with video, or 25 MP with Zeiss lenses. If you're willing to buy a used camera and accept a heavy battery pack, there's even a fully professional, weathersealed vertical-grip body in this price range.
Nobody has yet shown me a convincing 24x36 print from any "35mm" DSLR except the D3x - that doesn't mean nobody's printing them from the Alpha or a newer Canon - just that the prints I've seen from both didn't convince me of their ability to print that size (noisy shadows in particular - the Alpha files were from Sony, presumably converted from raw with their own converter, while I understand that many Alpha users prefer the results from other converters). I'm making 24x36 prints of detailed landscapes from the D3x, and other owners are as well. I'm sure that Canon (and maybe Sony) will release their own 24x36 capable SLR before long, although at least Canon's will probably be the same price. The 24x36 print size is a former piece of medium format territory that has now been invaded by at least one DSLR, and more shall soon follow.
I agree that the Alpha 900 is an amazing value in comparison with the D3x, but the D3x is itself a superb value against medium format. The image quality it offers is sufficient to print at any "normal" size, and it can replace medium format for many (most?) uses. The $8000 D3x is doing the job of a $18,000 low-end MF system. The $40,000 MF systems still stand alone and apart (and protected by the laws of physics) for the few applications that need them.
A bottleneck that we have already hit is "how large is your printer", and the closely related concept of "how large is the wall where you'll be displaying your prints". The bar for "35mm" image quality has cleared 24x36 inches, and, even if it never goes any higher (we see cheaper 24x36 capable cameras, NOT 30x45 capable cameras), 44 inch printers are very rare machines due to their great size (think upright piano), price and the amount of wall space their prints require. My iPF6100 is already a large and ugly piece of furniture that I have given up a corner of my workroom to because its prints are so beautiful, and I don't really want to meet the larger, heavier, uglier and more obtrusive iPF8100. Different photographers' tolerance of the demands of printers will vary, and some few will accept sharing their home or office with an iPF8100 (which I considered) or an Epson 9900. Others will decide that any printer larger than an Epson 3800 has a low spouse/partner acceptance factor.
Whatever your print size and needs, there is a camera out there that will meet them (and unless your print size is above 24x36 inches, it doesn't have to be MF). Unlike a few years ago, there aren't a lot of compromises in any digital SLR today that impact the images you make with it. They'll get better than they are today (more slowly than they have in the past, because the laws of physics are lurking in a dark alley nearby, waiting to whack unsuspecting camera makers on the head), but the improvements will be less and less relevant to the images we make with these tools.
When I remember back to my first digital SLR and printer setup (the Canon EOS-D30 (not the 30D - the original 3 MP D30 with the funky color space) and Epson's original Stylus Photo 2000 (the first pigment ink printer), and look at the 24x36 inch print I made yesterday, I realize how far we've come in the past eight years. It is now possible to make a print from a camera that looks like a 35mm SLR that would have required a view camera not that many years ago!
Where I'm more worried (and as a photography instructor at a university, I see a LOT of different cameras!) is with compacts. Digital compacts are rapidly LOSING features that would help photographers use them to make great images. Most compacts no longer feature independent aperture and shutter speed controls (a few years ago, most decent ones DID, even if they were inconvenient to reach), and I've seen a few this year that don't even have exposure compensation (and not $50 Kodaks, either). As the SLRs get better, and are good enough for more and more applications, the compacts seem to get WORSE! This is terrible news for photography teachers - our own cameras are wonderful, but what the students show up with is harder and harder to teach with (at least the cheaper SLRs mean that I see more and more of them, and can recommend them with a clearer conscience)!
-Dan
-Dan