Resolution is only one factor in the final image appearance. In practice, the D1x images are substantially better than those from a Coolpix 5000, assuming you're making large prints and taking all due care in producing them. The primary differences:
* The Coolpix lenses have substantial chromatic aberration in them. At high contrast boundaries you often get a red tinting on one side, and a greenish tinting on the other. The lenses are lower in contrast, too, at least compared to any of the f/2.8 prime optics you might use on a D1x. * The noise level of the Coolpix models, while good, just doesn't rival what you can pull out of a D1x NEF file, especially since the Coolpix's JPEG compression amplifies any small difference. * With a Coolpix you MUST get the camera settings right, because the camera renders the final image with them. If you use in-camera sharpening, or if you select a high contrast setting on a high contrast scene, you're stuck with that choice. Most D1x users who care about the quality of their image shoot NEF, which gives them the original sensor data and allows them to try different settings after the fact.
If all that weren't enough, most serious D1x shooters are using Bibble or QImage Pro to produce 10mp images from the sensor data--nearly double the resolution of the Coolpix 5000.
The Coolpix 5000 is a good camera capable of producing very nice results. The D1x is simply better, though.
Thom Hogan author, Nikon Field Guide author, Nikon Flash Guide author, Complete Guides to the N65, N80, and F100 author, Complete Guide to the Nikon D1, D1h, & D1x www.bythom.com
Thom Hogan author, Nikon Field Guide and Nikon Flash Guide author, Complete Guides to most Nikon cameras www.bythom.com