I agree with PaperCut Pro: it is simply the best icon creation tool I've used, period.
I have to deploy a set of 50-60 icons on a regular basis, and often after having to make small tweaks to several of them. Icon Slate makes that workflow, previously a nightmare, into a 30 second job.
One small flaw: Icon Slate does not create icons in the legacy compressed bitmap formats. I won't lower my rating due to this being a ridiculously small niche that I suspect few people want, need, or care about. For that part of my workflow, I'm unable to use Icon Slate, but it is worth every penny and more nonetheless.
The developer is incredibly friendly, knowledgable, and responsive. He's not a "celebrity developer" like some other folks in the Mac community, but after the conversation I had with him, he certainly should be.
If you need management for a boatload of icons (and don't have an obscure legacy requirement) you will not be disappointed with Icon Slate. I have no regrets about this purchase, and would have paid many times the price and felt the exact same way about my investment.