lyn: I think I slightly prefer RO4's uniform 'jigsaw' approach to the configure applications, and I'm not sure I'm fully sold on your drive icons.
Interesting that you should mention these two items in particular, because...
1. I was specifically asked to drop the jigsaw-puzzle outlines and do the Configure icons without borders, in the manner you see them. Though, whilst I quite liked the puzzle-piece shapes, I do personally rather like the style without them. As jigsaw pieces they do look somewhat regimented. I don't really have strong feelings either way; my point is just that this was something that Castle specifically asked for.
2. The drive icons caused a great deal of trouble - more than any other element, as I probably mentioned in my long article. That article does show a number of alternatives that were done, and I personally liked the 'bare hard drive' icons that I did first. (A few other people expressed a preference for these too - particularly the icon that looks a bit like a door bell!) Castle insisted that they looked too technical, though (people aren't expected to know what the inside of a hard drive looks like), and asked me to do something simpler. The icons we ended up with were the least objectional to the largest number of people, apparently, but I can't really claim to like them very much myself.
"I presume you're not able to currently distribute your iconset independently of the OS?"
Sadly not; they're the property of Castle. However, for anyone who owns an Iyonix, it's not difficult to copy them across to a RISC OS 4 machine and use them on that; there's a complete set of icons in the RO5 set, including ones that only Select actually uses. You just copy the !+Resource application over from inside !Boot (somewhere in PreDesk, I think) and delete the unwanted modules inside it, leaving just the two that define (a) the Wimp sprite pool and (b) the window tools.
"Finally, I'd noticed the '11Sprites' files in things like NetSurf - I assume these are the high-definition sprites you refer to. How are these currently used? Can RO5 display file icons at double size?"
It certainly can. Just edit the mode definition string for the current screen mode (availble from the Display Manager's icon bar menu) so that the EX and EY parameters are zero and click OK. You'll end up in a new screen mode, the same size and number of colours as before, but with big, double-detail graphics. (Obviously, you can do this for any mode; just edit the mode def string as appropriate.) It's a shame that there isn't a neater interface to this.