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I bought my D300s in January 2011 from Warehouse Express for £999 (pre-VAT rise) to replace a D200 as my main camera on an extended overland expedition in Africa.
The D200 was (and is) working fine but had suffered over two years hard use and I did not want to risk it failing and leaving me with just an old D70 as a backup camera.
I had been hanging on for the long awaited "D400" and had a serious look at the full frame D700 but took the plunge with the D300s on the basis that the "D400" did not appear to be imminent and as most of my pictures are wildlife typically at the "long-end" of the Nikon 70-200 f2.8 and 200-400 f4 lenses I was using, the APS sensor "crop" of the D300s was an advantage rather than a disadvantage.
Although the D300s (and in particular the MB D10 Battery Grip) feels more solidly constructed than the D200 (which was pretty good anyway), after a quick read of the instruction manual, it immediately ifelt like a very familiar.
Compared with the D200, the D300s battery life, low light sensitivity and image size and quality are all improved.
I have not made use of the video feature which for me is a "nice to have" rather than core function of a camera like this - I may change this view once I have had the chance to play with this feature.
A year on the D300s has still not been replaced and may be losing out in the pixel count wars compared with other Nikon cameras and those of competitors but still represents a very competent high end amateur/profesional camera.
This is my 3rd Nikon camera, I sold my d90 June 09 (bought originally body only for £650) and the d300s for £999 in Nov 10. for the difference in price.... the quality of the images does not, in my opinion, differ greatly. My favourite feature on the D300s which you didn't get with the D90 is the focus point and the choice of different focuses. Having Higher and lower ISO and a slightly higher shutter speed is also GREAT and totally worth it!. I also find HD video quality for better on this camera - although this isn't a feature I currently use very often. However other than those three features for the difference in price the quality of the image for me doesn't differ greatly considering the price. However this DOESN'T mean i'm disappointed with the camera in fact I love it especially the more use of focus points which is extremely useful for fashion photography.
However as i've entitled this "status over money" because I do believe owning the d300s for me was more about upgrading to a semi-pro SLR and having something in my hand that was more expensive was a state of mind that I wanted to give off, and say that I was progressing. If this wasn't my job, and it was a hobby without a disposable income i would have stuck with the D90. However I see this as an investment in my career and the slightly more high tech features listed above mean's i'm closer to the pro slr mark.
The perfect step up for anyone considering photography as a career. However a little expensive for those that "just want an slr"