All of the reviews I had done thus far are from items that I own or have owned. Generally speaking I don't review a knife until it needs a sharpening. When I get them I usually run them through some cutting tests, like paper and shaving, but I also give them a quick swipe on the Sharpmaker. Then I let them live in my pocket for a few months doing normal EDC tasks with them. Finally, once they have lost their edge, I sit down with the Sharpmaker and bring them back. No second sharpening, no review.
Well, ZDP-189 is presenting me with some problems. I have had my DF2 for a month now and I have used it almost exclusively and yet I can't tell any difference whatsoever in terms of is keen edge. I also didn't need to sharpen it when it came out of the box. So, I guess I will just have to wait. And wait. And wait. At this pace, the newest super steel will be released before my ZDP-189 blade dulls.
I can also report that it does excellent, even with its extremely high carbon content, with rust. It has been a damp couple of months here in New England and I can't find a speck of rust on the blade. It also is quite stain and tarnish resistant. I cut through an old pizza box and then didn't have a chance to wipe down the blade and the next day the grime came right off. Cardboard AND grease.
An early check on the steel tells me that it outpaces S30V by a noticeable amount in terms of edge holding. It is, thus far, just as stain resistant. I can't really find anything to complain about with the steel. It seems obvious to me, at least, that this is the new top of the heap. But you probably already knew that.
If I had to put them into tiers based on my three point scoring system (0=doesn't work; 1=works; 2=works well) with an eye towards edge holding, rust resistance, and durability (hardness v. toughness) it would be something like this (order in the tier from best to worst):
Top Tier (Score of 2)
Middle Tier (Score of 1)
Bottom Tier (Score of 0)
Buck Heat Treated 420HC
This is, of course, just my opinion, based on my own experience, but it seems pretty accurate with other people's experiences. For more on steels, see the link to Joe T's guide to the right.