I have the 9000's 35mm brother the 5000ED. I bought it for the typical reason, to digitize an archive of slides and negs that I have accumulated over the past 30 years. I bought the nikon because of an article in a british pub that described its qualities in a very positive light and the price ($1000 US).
The scanner and I didn't jive for about two weeks as I learned the variables that make it produce high quality scans.
I can offer the following that should apply to the 9000.
It takes a well exposed slide/negative to produce a good end product. Saving exposure mistakes is not doable. An underexposed slide can possibly be saved by another scanner but I seriously doubt that it would be of acceptable quality if your standards are high. Forget about digging out detail out of blocked up shadows/highlights. The 5000/9000 can bump up the light level to help if the shot is really necessary, but, the output is less than optimum. I believe this is true of all scanners.
If the slide is well exposed, the idea is to capture data as one would with a digital camera. Get it all. Don't do much post processing in the scanner software, but do it in photoshop. I do like the Nikon scanner ability to dig deeper with the scanner shadow adjustments but again don't overdo it. Nikon scans works fine within these guidelines.
With good data capture, the final output can really sing, if you approach it as one would a direct digital capture. Noise software, sharpening software (same programs as Michael recommends work super) etc. can make the output first cabin. I was really surprised with the output quality. Most of the comparisons I've read always seem to handicap the comparison with less than optimum conditions on the scanner side. Flatbeds or no edit or other processing is not a fair comparison to digital camera's.
I am amazed with the output I have gotten once I learned the rules.
The 5000 scan is tack sharp and you will get what is in the slide/negative. After that it's up to you. The 9000 should be similar. Just don't expect to output the scanner to your printer, but then you don't do that with your digital camera I suspect either.
I am truely amazed with some of the 16x24 prints from 35mm Provia I've output. I actually started shooting a little film again. I have to admit I like the film look. I actually started thinking about getting the 500 C/M cleaned and tuned again. It's been gathering dust for a while now. But then I would have to buy the 9000.