Nik software makes plug-ins that augment post processing.
In my own case, for instance, I use LR 3.3 as my RAW converter, where I also make basic and sometimes creative adjustments. In Adobe Photoshop (CS5 for me) I use its features, when necessary, to further develop my vision for the image and very often, but certainly not always, I use the plug-ins from Nik (and others, especially Topaz Labs) to further enhance the image. Nik's software will automatically add the adjustment into a Photoshop layer, which is helpful.
I currently use their Color Efex Pro 3.0, Silver Efex Pro, Viveza 2.0 and am just now learning their newest package, HDR Efex Pro. While I don't have enough experience with the the latter to say for sure, from what Tony Sweet and Jason Odell are saying in their new and excellent eBook on the software, one can do so much within the plug-in on a bracketed set, that little if anything (except sharpening) needs to be done afterward.
For me, the main pros of Nik's software is their U-point technology and the intuitive ease of their user interface.
I hope the above helps!
Phil