I use Nikon Capture NX2 almost exclusively for my NEF raw processing from the D700 & D3X. The advantage for me is the beautiful colour rendering and superb CA correction with not just current Nikon glass but also my Zeiss ZF lenses and older AIS glass.
The workflow takes a little getting used to, that I would definitely admit. The way that the application works by stacking adjustments (beyond the base camera/quick adjust/lens adjustments) can be quirky and confusing for new users, particularly compared to the way that ACR/LR/Aperture hide this. The other issue is the way that if you go up the adjustment stack and make a change you need to re-enable the stacked changes to render the full image. Not a problem once you know how it works.
The downside is that this rendering of raw through various transformations is pretty CPU intensive and they don't seem to cache to speed things along. On my 3GHz MacBookPro it is definitely not a fast process, although I find it usable when working on single images that I consider 'keepers'. On my 8 core MacPro it's a whole lot more usable. For rapidly processing a pile of files, other than sticking to the base adjustments, I'll sometimes use Aperture instead (I have no love for ACR's colour rendering, also Aperture doesn't support D3X yet natively).
As mentioned by another poster, for viewing your captures Nikon View NX does a pretty decent job and renders D3X 14bit NEFs quickly. It's much faster than the browse feature in NX2. There's a nasty bug in the current version though that sometimes produces an error 'File Format Not Supported' in certain zoomed/flip between images mode. I have to close the app and reload and it's fine - Nikon/Nik need to fix that NOW.
In summary, for me at least, Capture NX2 renders the nicest images in terms of colour, detail with essentially no CA. It is fair to call it slow, especially compared to the competition. It is however very usable and I find I can go through a standard workflow very rapidly just within NX2 for most images without need for further work in CS4. The local colour/contrast correction tools in NX2 mean that my Photoshop time is minimal and only needed where specific custom work is required.
$0.02.