Great shot and great reply. What´s the setting on sharpness on your camera?
Since I shoot RAW/NEF is do not add any in camera sharpening or any other in camera settings. No need too. All in camera settings sliders are in the middle which, I think, is default on the D90. Now, this image I posted is about the sharpest image I have ever taken in my life. Most others are not this crisp but I have gotten a good few lately (due to awesome coaching from people on this forum whose images I admire greatly).
So I will try to pass on what I have learned. The D90 is a great camera. I love it dearly. However, at 12.2 megapixels its images are not as dynamic as an FX sensor camera but if shot right it will be difficult for most people to tell.
Depending on your lens, or the lens you use at any given time, there will be a sweet spot for that lens. It may be at the longer end of the zoom or shorter end. Usually somewhere just shy of the two extremes and somewhere in the middle as well. Not full zoom out or in. Aperture plays such a huge roll in sharpness as I found out. Somewhere between f/6.7 and f/11 will likely be the best choices for aperture. Keep shutter speed as high as you can. Keep ISO at or lower than 800. D90's can get noisy/grainy at higher ISO than 800. Don't sacrifice aperture for other settings though. Keep it in the middle if possible particularly on anything that is farther than a few feet away from you or something that is moving. Leave wide open aperture for portraiture or still shots.
Check your lenses at all apertures, zoom ranges and different shutter speeds and find that sweet spot. Make sure you have enough light to keep things in the good zones.