I wanted to just say a little bit about the "grow into" it thing. I don't think it is an entirely "bogus" argument.
In digital, I've owned a few point and shoots, a D70, a D80, and now a D300. I think there are some real image-quality differences between the D80 and the D300. The meter in the D300 seems to be more accurate and the autofocus seems to be a bit better. Noise seems to be better with the D300 at higher ISO. I love the saturation I can get with the D300 that isn't possible with a D80. I also like the active D-lighting. JPEGs straight out of the D300 usually require much less adjusting than those from the D80 (yes, I'm a heathen and usually shoot JPEG over Raw unless it's something really important).
Don't worry, you're not a heathen for shooting JPEG. Most pro shooters i know and work with shoot JPEG unless they know for a fact it's going to professional output.
I have to agree with compuwar on this one. The comment "grow out of/into" is one that is thrown around a lot when people want to justify getting the latest and greatest gear. I am sorely upset with a lot of D300 owners right now, their images are still just as mediocre or bad as they were when they had their D70/D50/D80/D200 bodies. Their skills didn't change, and as they would put it, they didn't out grow their bodies.
The D300's IQ is great compared to the previous gen, but if you weren't able to get that kind of quality out of the previous gen then you were doing something wrong, and the D300 won't help you in any way other than doing the work for you.
The D80 is actually the only body Nikon has produced that meters just as accurately as the D200 and D2xs. It's actually spot on, more so then the D2hs. I have these bodies by the way, and if I don't need the speed then the D80 would go before the D2hs. Noise is better on the D300, yes, but if you can't shoot up to ISO 800 on a D2-- series without getting noticeable noise it's a problem with the shooter. Above 1000 and the camera's limitations come into play, I agree, but there are ways to compensate.
The saturation on the D80 JPEGs is about the same from my POV. I can't argue with that since it's my opinion, but the JPEGs rendered from the D80 and D50 are better than the ones I get from my D200/D2hs/D2xs, that's where that body was intended to perform well. RAWs on the other hand are the opposite.
When a beginner wants a D200/D300 to start and their reason is "I want a body I can grow into" it's just not a valid reason. If they want it because they want it then fine go and get one if you have the cash to blow. But as I told the 5D buyers that got cheap glass, that D300 is going to give you soft, mediocre images if you have a cheap kit lens on the front. And by kit lens I do mean the 18-70 DX and below.
Nikon makes 4 top notch pieces of glass, and once you shoot with them it's hard to consider anything else (in the DX line) as NOT a kit lens. The D80 and 17-55/70-200VR/18-200VR are quite good performers and yield IQ that will rival that of the D2xs. The only thing left out of the D80 is the 5 fps and autofocus speed. If you aren't shooting a lot of sports and getting paid for it then it's not that important.
Unless you have the cash of course.