adh1003: "IMHO, it will be entirely possible to build a box using open RISC OS components and sell it. You would have to pay a unit royalty to Castle, but that would be your one and only notable restriction."
It's worth noting here that the one and only notable restriction, whilst it may sound like "just a few quid on the retail price" to some people, is less a financial restriction and more one of control. One major difference between some GPL+proprietary dual-licensing scheme and this one is that in the case of a proprietary licence being denied to a vendor, any released software must become perpetually non-commercial; thus downstream recipients of such code have to be careful not to profit from providing the code to others.
steelpillow: "This shared source license looks at first glance very similar to the kind of thing that MySQL, KDE and so on do, I'm not sure why some people think it is different."
It is different because even permissive open source licences do not distinguish between different fields of endeavour. And even the GPL focuses on the social contract aspect of keeping the source available to everyone, not on insisting on non-commercial usage, but that's because the FSF isn't about preventing people from making money: it's about preventing people from exploiting end-users by withholding the sources.