Keep in mind that hardware OR software, the placement is paramount.

Normally, you want to denoise, hum, click, pop, etc. before you do ANYTHING.

It's hard enough trying to take noise away when it's very steady - It's damn near impossible once the mix has a compressor on it varying the levels of the noise. Once the gain level has been established, it's time to work on the noise.

Personally, I don't know of many units (hard or soft) that do a really decent job. Waves restoration tools are fairly good in the software world, but nothing's perfect. If I can, I just try to notch out sharp noise or gently subtract soft noise using EQ.

I hope to hell I don't have to do noise reduction in mastering. Means that something really bad happened in the recording (although, the orchestral stuff I have worked on that was mixed and tracked on a Euphonics System 5 digital console has often needed it).

Depending on what the situation is, I have a few different methods of working. My own rig is based around Sequoia and the TC Powercore restoration suite. The TC suite is decent, but not fantastic. I get my best results when using it for small amounts of noise removal and in conjunction with the tools that come with Sequoia.

When the client has the bucks for serious work, I bring it to a seperate studio either based around Sonic NoNoise, Cedar, or the new Algorithmix Restoration plugins. For ease of use and speed of work, the Algorithmix is hands-down the best thing out there. The tools are of VERY high quality and to be able to work in the plugin realm is quite nice, indeed. NOVA is nothing short of genius. NoNoise and Cedar are fantastic tools as well, but often take more time to get the desired result (Cedar requires a pass-through in real time).

Even when you have high-end tools, it still helps to have mulitple tools at your disposal as some will work better than others. One may work for the broadband noise reduction and another may be better at buzzes or clicks... It really depends on the program material.

--Ben