I haven't tried the other Pentax digitals so I can't offer a comparison, but I have been using an ist-D for two years now and can offer my thoughts on that. This comes at a good time because I've been wanting to put my thoughts on the subject into words for some time now and it seems as if an opportunity has arisen here!
What occurred to me a couple of months ago was this: I believe that I've gotten more satisfaction out of the ist-D than any other photographic product I've ever purchased, lens or camera, film or digital. After two years I still marvel at how good a product it is. Though I expect most people on this list have a fairly low opinion of Popular Photography magazine, Pop Photo really hit the nail on the head when they wrote that the ist-D feels so well developed and thought out that it's hard to believe it's Pentax's first production DSLR: Of course it's not perfect, but functionally it works as well as you'd expect from a product in its second or third iteration. So high is my regard for this camera that my main concern about its upcoming replacement is that Pentax doesn't screw up any of the things is got really right with the ist-D. Of course we all know some of the things we can expect from the replacement DSLR: More megapixels, lower noise, bigger/faster buffer, in-camera image stabilization and probably some other features that haven't leaked out yet. I just hope we don't lose the things that make the ist-D such a winner: Separate aperture and shutter speed control wheels, AA battery power, optional detachable battery grip. The battery thing is sheer brilliance, IMHO. With the battery grip attached you get double the power supply and extra grip area and leverage for big lenses. With the grip removed you get a diminutive camera that you can carry along when other DSLR's would stay home. When I was bicycling France last September the ist-D, usually with the little 43mm Limited, was hardly noticeable in the Tamrac bag slung around my neck. Mid-week I tried to go one day too many without recharging the batteries and the camera dies on me around 10:00 in the morning. So... I'm in rural France on a bicycle and my DSLR's batteries have died. What now? I just stop at a drug store in the next town we come to, buy four AA lithium batteries and I'm off again. The image quality, with good quality glass, continues to impress me. The viewfinder is outstanding in its class. It accepts my 30-year-old Pentax lenses. I can't say if anyone else will be happier with an ist-D than any of the other Pentax DSLR's, but I can say that I have no plans to part with mine even after I get the replacement model later this year. -- Mark Roberts Photography and writing www.robertstech.com