Well, many years ago, I was in Cam Workshop and saw a guy spending S$8500 on a 'N' brand camera with a lens. He had to spread it onto two credit cards because one could not get thru. The very same camera is today, ahem, worth less than S$200. You can still find many new ones on E-bay but no body will buy them. One can argue the camera was used a pro tool, but for the nature of the photo business, a $8k basic tool is really over the top.
Same as today, many D90 started to get dumped in the dumpsters' market. Many are still asking for over S$1k for a used package, which in reality you can buy new from USA mail order for much lesser than that price. So punters beware of dumpsters. Why D90 is falling out of grace, is a rumoured D95. People have yet seen the D95 and already are dumping the D90. Such is the fate of modern DSLR.
Comparatively, the Pentax K-x is a camera that is perfect for hobby and semi pro use. I have seen many using it to make money in US for event photography. Using a cheap but very effective tool to make as much money as possible is very good sense.
Pentax is backwards compatible to screw mount, M and even A lenses. So one has a lot of cheap and good lens choices (significant increase in prices for old lenses). I personally see no meaning in spending more money buying a D300 or k-x using the same Tamron 17-50 DX zoom lens. For me, the applications comes first, then the choice of lens and finally the body. And incidentally, a film body meets the picture picture quality of many expensive DSLR.
I knew of a pro photographer who used the Nikon N2002 (many of them) in all his career. He put thru more than 1000 rolls of film per quarter, and ran the cameras to the ground. When doing golf photography, the film camera and the traditional develop/print meets the process requirement (you finish shooting about 8 rolls at 2pm, and need to distribute sorted pictures to more than 50 guests by 6pm. Imagine you have to download 300 raw or jpg pictures, edit and print them in 3 hours. No thanks. His gears were nothing special, just the simple 35mm for group photo, and the 135/180mm for golf shots. In this case, whether N C or P brand anyone can do the job more than adequately. In fact, his pictures will the appropriate fill in flash were always very impressive, and made him a lot of money with several clubs.
We should be happy that k-x is selling for less than S$800 locally. Use it to the max. I suppose K5 and a K7 are coming out soon. But on paper, fortunately, will not obsolete the k-x. Enjoy Pentax.