I find myself drawn to the PENTAX cameras by the weather-seal issue and the bang-for-the-buck factor. But I hesitate due to the modest market share and lens selection. I'm most interested in landscape and city-scene photography, and would like to experiment with shooting live theatre. Right now, I'm probably looking at the K200D, possibly with an upgrade from the kit lens. K20D would be a bit of a stretch.
I often do similar photography, cityscape and landscape, with Pentax as my SLR system. I'll also shoot medium format film when I feel like dealing with lugging a tripod around, getting film developed, and then scanning it...
Do you ever regret you decision to go with PENTAX?
Yes and no. I went with a Pentax DSLR because I had an old Pentax film SLR (1970's vintage) with a lot of glass -- all fully manual stuff, but that didn't bother me. As I've grown as a photographer over the past few years, I've augmented that with more modern lenses, autofocusing and all that, and moved from a *ist DL body to a K10D.
The no regrets first -- the K10D doesn't autofocus as quickly as a D3, but it's adequate for my uses. I very rarely do any sort of sports or wildlife shooting. When I do, I generally use my only zoom lens (the DA* 50-135mm), which has an in-lens motor -- it seems to lock on faster than lenses that use the screw-drive for autofocus.
Also, I'm a bit of a lens snob, and I'll be the first to admit that. The FA 31mm Limited is on my camera about 85% of the time. I use the 77mm when I want to go longer, and actually just got the 43mm this week, but haven't got a chance to shoot with it yet. The rendering characteristics of the 31 & 77 are very special -- I can't always put my finger on it, but the color reproduction and contrast that these lenses produce just really suits my sense of aesthetics. Images I've seen taken with the 43mm also represent this, and I'm hoping to get some first-hand experience with it this weekend.
For really wide-angle landscapes I generally use the DA 14mm, which I'm actually thinking of getting rid of. Everything I've seen shows the 12-24mm to be just as good in most situations, and I really don't need the extra stop for something that wide....
Now, the regrets --
I'd really love a DSLR with full 35mm frame coverage. The crop-sensor on the Pentax turns the 31mm into a normal, the 43mm into a short-telephoto, and the 77mm into a longer telephoto. As more of a wide angle guy, I'd prefer to have that trio represent wide, normal, and medium-telephoto fields of view. This is why I keep a film body & a few rolls of Provia in the fridge.
The viewfinder. Ugh. This isn't a Pentax problem, it's a problem with DSLRs that aren't the D700, D3, 5D and 1ds Mark whatever (sorry A900, I was not impressed when I looked through your finder in comparison to the Nikons). I can't accurately manually focus with it. I had the Zeiss 50mm in the Pentax mount to evaluate for work and it was very difficult for me to nail focus consistently -- a problem I never have on a film SLR, medium format, or rangefinder. I really should swap out the focusing screen for a split-prism type, but for whatever reason that just hasn't happened yet.
Are there deficiencies or limitations you wish you had known about before you made you choice?
Nope. I did my research. You're doing yours, so hopefully you can answer that question the same way!
Are there circumstances where you'd recommend against going with PENTAX?
Do you need full frame? Do you need an f/2.8 zoom that is longer than 135mm? Do you see yourself shooting a lot of fast action where fast autofocus and long burst shooting is critical?
Those are the weaknesses. The strengths are in optics -- the aforementioned 12-24mm f/4, the 16-45mm f/4 (a great, budget-conscience alternative to the kit lens), the FA Limited triplets.... as well as compact optics if weight is a concern (the DA Limited primes -- 21mm, 40mm, and 70mm).
I'm not a telephoto person, but you have the 50-135mm f/2.8, a 200mm f/2.8 and 300mm f/4. The unicorn-esque 60-250mm f/4 should be out this year (although put me in the "I'll believe it when I see it category" on that one).
Also, if you ever want to do macro, the DA 35, FA 50 Macro & FA 100 Macro are all very good lenses.... and if you want to break the bank, the Zeiss 100mm f/2 macro is available in the K mount, though that's another case where you would want to install a split-image focusing screen for any serious work.
And then there's ergonomics, but that's a personal preference -- but if the lens line-up suits your needs, and you like the camera, and it suits your budget... well, it's your money to spend.
And if you're not making a serious serious investment in glass, then don't let market share bother you too much. If it's the body & a lens, the prospect of Pentax going under (I don't see it happening in the near future) or the K-mount going away (which would require Pentax to go under & Samsung to give up on the DSLR market).
Hope this helps.... any other questions, please feel free to ask...
Jim