Re: Shaptons and Sigmas
Pam Niedermayer
Note: So far as I know, I have only carbon steel edges at this time, so no consideration for A2, HSS, PM, etc.
I bought the Shapton 2000 and 5000, as well as the lapping plate, very shortly after Harrelson started reselling them, probably in 2002, the same year I started investing seriously in Japanese tools. But I had mostly western edges which I sharpened using sandpaper, grinder, black Arkansas, and leather strop with green. I planned on inserting the Shaptons into roughly the midst of what I had, and also bought an Aoto Mountain Blue for the bridge between the 2k and 5k Shaptons (which probably didn't exist, but it was so pretty).
So, I started sharpening these new eastern tools, and all went pretty well. I dropped the grinder for them and seldom used the black Ark. I really knew nothing much about sharpening, so when I started trying to sharpen my western tools on the Shaptons, I was floored with the stiction after a stroke or two flattening the backs. They were unusable. Now I know there are a couple of things I could have done, but I was so pi__ed. All that money on waterstones that only worked on my few eastern edges. To this day it makes me sick to even look at them in the cabinet.
And I was only saved by the city that issued a stop work order on my shop rebuild, but since I decided to ignore that a couple or four years ago, I've added to my eastern tool collection significantly (to be honest, I also added eastern tools pretty steadily since 2002) and managed to get excellent results from natural waterstones (including the Aoto that's still beautiful).
Now to early this year when I started reading posts about the Sigma Power ceramics. They could solve the problem of not being able to create a real sharpening system with the natural stones. There are always one or two stones that don't work with one or five edges, and this is kind of disruptive. So I bought the SP 1-6-13k set from Stu and I've started testing them with a few edges, with a Tsunesaburo extra large kanaban (from JWW) and White Alumina (thanks, Stu) for back flattening. Generally I'm very pleased with them, they are far superior to the Shaptons, and with the addition of one or two more stones (SP 400 for one), I think I may be on to something special. They feel like regularized natural stones, and they work great with my western edges. One of the reasons I chose the SP's is I plan to make some PM chisels real soon now; and the SP's are supposed to handle PM with aplomb.
But, I won't be ready to make recommendations for quite some time, maybe the end of the year, if then. I guess I have a natural reluctance for proselytizing, describing systems, and writing long posts. And since I'm only an average user, nothing I would have to say about Shaptons is relevant. 
Pam