Nikon Capture NX is Nikon's replacement for all prior releases of Nikon Capture. They will not likely make future enhancements to Capture 4.x and older. Any new cameras (D3 series, for example) likely will be only supported by NX, and future capabilities of NX likely will not be available to users of Capture 4.x and earlier. There are already features in Capture NX (like point controls) that are not available in Capture 4.4.2. Keep in mind that all of the changes made to NEF files with Nikon software are not consumable by any other software. Other software will still be able to read the original raw data in the NEF file, but it won't understand any of the post processing NEF changes you make with Capture.
I own Capture 4.4.2, but rarely use it. I can get the same quality out of Adobe Camera Raw and it fits better into my workflow with Adobe Bridge and Photoshop CS2. After setting up my raw conversion parameters and adding my meta data, I convert all my raw files to DNG format, which makes them incompatible with the Nikon software - but compatible with so much more software that the NEF files are incompatible with.