As I have a Nikon camera, it seemed a good idea to check out Nikon's photo editing program, Nikon Capture NX 2, so I downloaded the free 60 days' trial and played around with it a bit.
It seems a decent, competent program at a modest price, though relatively early in its development, compared with programs that have been around for years.
However, if you buy it as your only photo editing program, bear in mind that it concentrates on photographic functions and misses out a lot of more general image editing functions that you would get with Photoshop or even Paint Shop Pro. As someone pointed out elsewhere on the Web, what if you want to write some text on top of the photo?
If you have Photoshop already, I see little point in buying Capture NX 2 as well. As far as I could tell by experiment, Photoshop imports Nikon's NEF files as well as Nikon's own program does, and provides more editing functionality.
The Nikon program offers the unique functionality of U Points, otherwise known as control points, which are a cute way of making local changes to parts of a photo. This could well be of interest to some people, but it's not my style. I feel happy manipulating a photo as a whole, but I don't want to get into messing around with parts of it.