"It's the photographer, not the camera or lens. The camera is only a tool: the image is the product of your mind and vision."
This has been my motto since I began shooting with digital. The reason for the above statement is to show people that there are viable alternatives to using a camera system from the "big two". My tools do what I want them to - that's all that matters. I've also shot with the Canon system, and it can be a superb setup in most (but not all) conditions. All camera systems have strengths and weaknesses.
I chose Pentax simply because the K10D/K20D bodies and battery grip are weather-sealed. This is very useful when shooting for days/weeks in the outdoors. The newer DA* series lenses are motor-driven and weather-sealed. I don't have to worry about their performance under optimal or harsh conditions. The image quality is breathtaking, and the contrast and color of the optics are stunning. I primarily use a mix of older film (the professional FA* series) and newer digital specific (DA series) lenses.