I have a love hate relationship with Nikon's software, I love the image quality and hate the speed, or lack of speed. For difficult product images in which color fidelity is critical, Nikon Capture 4.4.2 is our standard, it just renders the file the most accurately for our work. For example, I have a client with a product that has 16 shades of tan leather. When that kind of mind-numbing color control is needed we use Capture or Capture NX, it just extracts the most accurate rendering of the Nikon RAW file, which in turn, converts to the printing profile with the least amount of color shift.
I have just recently done a job in Nikon Capture NX. As Dierk stated, working in NX's base adjustments is just like working in Capture 4.4.2 - SLOW. However, Capture NX allows the use of Edit Steps, similar to adjustment layers in Photoshop, which render much faster. I found an excellent post on the Nikonians website detailing the ins and outs of Capture NX, it's well worth your time:
http://www.nikonians.org/cgi-bin/dcf...um=DCForumID36
I have also found my way to the same level of color fidelity with Capture NX that Capture 4.4.2 has provided, so batching a shoot into 16b tiffs is faster and just as accurate. The color control points are very cool, and can be set into a batch process as well, just like any other Edit Step, which works well for images shot in a similar setup. Once you get used to where the tools are that you use most, I think you'll enjoy working in Capture NX.
For sheer speed, when color fidelity isn't critical the Adobe Camera RAW or Lightroom spank all of the Nikon products. When I say color fidelity, I'm not talking about colors that are pleasing, I'm talking color that converts well to offset lithography printing profiles. Again, my client with 16 shades of tan!
And to the original post, I have found the upgrade to a Core 2 Duo machine worth the investment.
Hope that helps
Mike