I use both ViewNX and Capture NX 2.
I find ViewNX the most useful for all quick adjustments such as exposure compenstion, picture control, D-Lighting etc. I only go to Capture NX for things like getting rid of a bit a annoying back scatter, cropping, straightening and other more sophisticated adjustments. The Auto Retouch Brush is very good, a bit like the clone stamp in Photoshop but esier to use.
I try to avoid using Capture NX unless I really have to because once you have adjusted a photo in Capture NX you can no longer use the ViewNX Convert Files facility to do your jpgs.
Capture NX 2 is not in the same league as Photoshop but if you are a purest and believe in the minimum messing with the original photo, then it is OK for those minor corrections.
Cheers
Treb