As with most things photography related, my opinion is that it really depends on your own needs. I honestly have nothing against a dinosaur...I still have my old Sony H1 (5mp) and I still use it on occasions where I won't bring my DSLR's (such as in a canoe). It goes without saying that the D200's/300's have a rather loyal following, however I would suggest a bit of discretion regarding the replies...they're decent cameras, however they're not the end all/be all bodies that some people like to believe...going on about how rugged they are doesn't mean other models are "cheap" by any means and all the extra knobs and dials can be extraneous to someone who doesn't need them. When I switched to Nikon a few years back, I actually went with the D90 myself and when I got a "new to me" body recently, I went with a used D7000...both were over suggestions of the D200's/D300's. In my case however, while I don't (usually) need a rugged body built for extreme environments and have little use for the super fast shutter speeds, I -do- need those low light capabilities and I also do use the video as well...I have other camcorders, however none of them produce the "cinema-like" quality of my DSLR's, so for myself those were huge factors. In my case, a D200/D300 would have been a poor choice...that said, obviously my own needs and priorities are different from others.
Since we're talking about used cameras here, the one piece of extra advice I would offer is that if you're comparing a few different cameras, do ask about the shutter count. If you have 3 otherwise comparable bodies (all the same make), assuming they are comparably priced, go with the lowest shutter count. In short, you don't want to end up with a camera body that is nearing the end of it's life expectancy. The D200 for example is only rated at 100,000 shutter clicks, so being older/used cameras, that's something you'll want to pay close attention to as any repair cost is likely to exceed a better replacement body.
BTW...for what it's worth, while I will occasionally use jpeg for shots to use on Craigslist or
Ebay, any serious work I do is ALWAYS in RAW. As far as I'm concerned, there just isn't
too much advantage to shooting in jpeg...anything your camera can do in jpeg, you can do in post and convert later if needed. Regardless of the body/brand/make, RAW just gives you FAR more flexibility for processing your images.
So with that said, again I think it depends on your own specific needs. If you're comfortable with the comparatively limited capabilities of the D200 and as others have suggested, you can find one in decent condition that hasn't been beat on/abused (a different issue in itself), then go for it. Just because it's less than bleeding edge doesn't mean it's useless.
