I cannot speak for Nikon gear but, I have purchased several cameras (30D 40D and 7D) and a lens (40mm f/2.8 pancake) as Canon refurbished items (from Adorama and from Canon directly) and have been extremely satisfied with both the price and quality. I am still shooting with the 30D and 40D that I purchased years ago and have had no problems.
OTOH, I needed to send back each of the two DSLR cameras I purchased new (10D and 350D) within the first 90 days of use...
I own a lens which I purchased new that had to be sent in for repair 3 years into the 5 year warranty, so in a way it is a refurbished lens. However, most refurbished gear did not get that designation because they were repaired. Some are return to stock items or discontinued items.
Right-on, John... However, all OEM refurbished gear has been checked by a technician at the manufacturer's service center before being sold as refurbished. New gear is often never checked by a human.
BUT, an this is a big BUT! A piece of gear which was returned to the camera store, given a quick once over by a salesman and then sold as a "refurbished" item is NOT what I am talking about.
FYI, it's also worth looking at refurbished computers when you're ready to buy. In many/most cases these are computers that were returned unopened (e.g., wrong order or the buyer changed his/her mind) and have never been used. They are checked and restored to factory condition and in many cases carry the same warranty as a brand new computer, typically for $100 or more off the price. I only buy refurbished computers now, direct from the manufacturer, and have never experienced any problems. The only downside is that you have to buy what's available, so if you typically have your computers built to order this won't work for you. But I never get built-to-order computers; I can usually find a standard configuration that meets my needs.